Thank you all for your answers.
I will try the advice from @dobey when next Hybris/stable release is available. (I don't use devel channel anymore because it is not stable enough for daily use of the phone...)
@hengyedev I haven't been able to get updates to work on my phone, but I have just realised that I only temporarily had TWRP on the phone, I never fully installed it (I used the Lineage OS install guide in conjunction with your guide to install Ubuntu Touch: https://wiki.lineageos.org/devices/kirin/install ) So, the phone doesn't have TWRP on it after I installed Ubuntu Touch (I assume it just has the stock recovery [if there even is one] still installed instead).
Should I properly flash TWRP to the phone? to ensure that the updates that the phone downloads actually install properly. As they seem to download new 'versions' but whenever I click 'Restart & Update' the updates don't get installed to the phone.
Not having this device I can only go with what @AntiDroid said that there will be a way of reinstalling android if you wanted then retry the installer. You may also be able to install TWRP for your device then run the installer. One last thing I see the installer only lists the 771 not 712. Knowing how specific the installer is and not knowing anything about these tablets I would double check that is not an issue if yours is a 712.