But instead of the recovery menu, I was greeted by the spiralling animation: the phone was clearly installing something. When it finished rebooting, I was back on OTA-20, and both SIMs were still active!

Following @DPITTI suggestion, I also removed v763 from the upgrade history.

I'll now mark this post as "resolved". Many thanks to all those who contributed.

What I would like to add to the updates. If you are using a mobile phone with low data volume, please make sure that you set the settings to Wifi only or a data connection. Some people are surprised when only the circle turns. I have read this several times now, so I would like to mention it here as another problem solution for failed updates.

Greetings Mario

@phandersson So you are back on stable with 2 simsworking?

The 2 SIMs are working again, yes, but I'm still on "devel" (v763), and apparently unable to get back to "stable". I can select the channel, but nothing gets downloaded.

Might just be an overlap of updates between being on dev and going back to stable. Should be safe enough to ignore it and carry on the next stable update should remove it.

You mean, switch to "stable" even if nothing happens, and wait for OTA-21 to be released? I can try. Although representing heavier work, I guess I could also re-install the phone from scratch on OTA-20 using UTI.

By the way, the problem of dual-SIM support in OTA-20 is a known bug (just found out about it):

https://github.com/ubports/ubuntu-touch/issues/1879

...and a manual fix is provided in the post by "laguna66".

What's strange is that after switching back to the stable channel, the main "Settings" screen shows 1 update available (see screenshot below):

But when tapping on that line, and after "checking for updates", it still returns "Software is up to date".

I'm happy to report that this restored access to both SIM slots -- see screenshot below:

I'll now switch back to the stable channel and report again.

If you are on OTA20 yoh will not get a new stable version until the next OTA is ready.

I disagree, the procedure I described works in my case - Xperia X and Mi A2.

@PhAndersson
If you are unlucky with it, do what @Lakotaubp said.

Right after switching to the "dev" channel, the phone downloaded a 500MB installation image (which I didn't actually install, obviously), but once I returned to the stable channel, nothing more happened. It still shows the dev image ready for install, but nothing new for the already installed system (see attached screenshot).

Likewise in "About | Check for updates" -- it checks, then shows the exact same thing.

Just upgraded to OTA-20: the upgrade process itself went flawlessly, but the SIM card in slot #1 is no longer detected!

Hi, I faced the same problem. I remember it was upgraded via delta, not full image. After full image "re-upgrade" two sims appeared in my case.

You can try this: Through the settings change channel to devel, close settings, start settings again, there should be devel upgrade available, don't upgrade and change channel back to stable and close settings again, now when you start settings there should be stable upgrade available - full image (cca 500 MB). Do the upgrade and you will see.

cc00000.qcom,vidc:firmware_cb
dbmd4_va_fw.bin
dbmd4_va_preboot_fw.bin

adsp.mdt (/devices/soc/15700000.qcom,lpass/firmware/adsp.mdt)
adsp.b02 -> adsp.b23 (/devices/soc/15700000.qcom,lpass/firmware/adsp.b02 -> ...)

a530_pm4.fw (/devices/soc/5000000.qcom,kgsl-3d0/kgsl/kgsl-3d0/a530_pm4.fw)
a530_pfp.fw (/devices/soc/5000000.qcom,kgsl-3d0/kgsl/kgsl-3d0/a530_pfp.fw)
a512_zap.mdt (/devices/soc/soc:qcom,kgsl-hyp/firmware/a512_zap.mdt)
a512_zap.b02 (/devices/soc/soc:qcom,kgsl-hyp/firmware/a512_zap.b02)

cdsp.mdt (/devices/soc/1a300000.qcom,turing/firmware/cdsp.mdt)
cdsp.b02 -> cdsp.b07 (/devices/soc/1a300000.qcom,turing/firmware/cdsp.b02 -> ...)

cmnlib64.mdt (/devices/virtual/qseecom/qseecom/cmnlib64.mdt)
modem.mdt (/devices/soc/4080000.qcom,mss/firmware/modem.mdt)
cmnlib64.b00 -> cmnlib64.b06 (/devices/virtual/qseecom/qseecom/cmnlib64.b00 -> ...)

mba.mbn (/devices/soc/4080000.qcom,mss/firmware/mba.mbn)
msadp (/devices/soc/4080000.qcom,mss/firmware/msadp)
modem.b02 -> modem.b28 (/devices/soc/4080000.qcom,mss/firmware/modem.b02 -> ...)

tas2557_uCDSP.bin (/devices/soc/c1b6000.i2c/i2c-6/6-004c/firmware/tas2557_uCDSP.bin)
wlan/qca_cld/WCNSS_qcom_cfg.ini (/devices/soc/18800000.qcom,icnss/firmware/wlan!qca_cld!WCNSS_qcom_cfg.ini)
wlan/qca_cld/wlan_mac.bin (/devices/soc/18800000.qcom,icnss/firmware/wlan!qca_cld!wlan_mac.bin)
cpp_firmware_v1_12_0.fw (/devices/soc/ca04000.qcom,cpp/firmware/cpp_firmware_v1_12_0.fw)
venus.mdt (/devices/soc/cce0000.qcom,venus/firmware/venus.mdt)
venus.b02 -> venus.b04 (/devices/soc/cce0000.qcom,venus/firmware/venus.b02 -> ...)

I found out 2 ways to start investigating this issue.

1./ firmware versions
In a recent post (https://forums.ubports.com/topic/6813/unable-to-turn-on-bluetooth-on-mi-a2/29), @nauvpp mentioned upgrading the bluetooth firmware on his device from an archive bundle called firmware_jasmine_sprout_V11.0.28.0.zip. I've downloaded that ZIP and looked at its contents, but how can I check whether any of the .img files contained within are more recent than the ones already on the phone?

2./ 'dmesg' output
I collected the dmesg output after the upgrade (unfortunately, I don't have any example dating back before the upgrade, so I can't compare).

In there, searching for the "radio" keyword, I see the following messages:

[    5.226487] init: Received control message 'interface_start' for 'android.hardware.radio@1.0::IRadio/slot2' from pid: 28 (/system/bin/hwservicemanager)
[    5.226518] init: Could not find service hosting interface android.hardware.radio@1.0::IRadio/slot2
[    5.226602] init: Command 'exec_start update_verifier_nonencrypted' action=late-fs (/init.rc:390) took 0ms and failed: Service not found
[    5.226747] init: Received control message 'interface_start' for 'android.hardware.radio@1.1::IRadio/slot2' from pid: 28 (/system/bin/hwservicemanager)
[    5.226763] init: Could not find service hosting interface android.hardware.radio@1.1::IRadio/slot2
[    5.226861] init: processing action (post-fs-data) from (/init.rc:392)
[    5.227228] init: Received control message 'interface_start' for 'android.hardware.radio@1.2::IRadio/slot2' from pid: 28 (/system/bin/hwservicemanager)
[    5.227257] init: Could not find service hosting interface android.hardware.radio@1.2::IRadio/slot2

[   13.012729] init: Received control message 'interface_start' for 'android.hardware.radio.deprecated@1.0::IOemHook/slot2' from pid: 28 (/system/bin/hwservicemanager)
[   13.012794] init: Could not find service hosting interface android.hardware.radio.deprecated@1.0::IOemHook/slot2

The first message block repeats 3 times. The second block occurs only that one time. But is this relevant?

Coming back to my "firmware" line of thought, I see a lot of firmware modules being loaded (often with some hint about their version), but do you have any idea which one I should be looking for?

Which Android did you install back then? It says something about Android 9 in the device link. I don't know for sure as I have Xiaomi Redmi Note 9. But even here I had to downgrade to Android 10, because I also had problems with the SIM card at the beginning. I would have tried to reset the system to factory settings after the update. If that doesn't help, test the available channels for the software. Sometimes it also helps to gently clean the SIM card with alcohol. Or simply switch flight mode on and off or reboot several times. Otherwise, wait and see what others say.

• during startup, I'm prompted for only one PIN code (the prompt no longer identifies the SIM, but the code only matches SIM #2)
• in "settings | mobile", only one SIM and matching operator is listed (the one for SIM #2)
• same thing in the top-of-screen quick access bar
• "setting | about" reports OTA-20

Is there any information I could collect on the phone to help troubleshoot this?

I'll apply OTA-20 in the coming days and report back.