There might be minor hardware differences, too. At least on Pixel and Pixel 2 the XL variant has a different build tree with some incompatible differences.
@givemeaname sounds like a faulty cable to me then. On my Nexus 5 it also sometimes has issues with losing connection, but normally the installer resumes as well if the cable isn't super bad.
@freefrog Thx for answering. I allready switched to google free android since I needed to use my phone. I will try to reinstall Ubuntu on weekend and tell you if it worked.
Sadly Miracast support still needs some work on Android 9 based devices. I'm sure it will get there but it's not working right now. Still, it will be the only way to support external monitors.
@antidroid thanks for looking into that. A rather odd design decision but happy to know that also means they likely used an earspeaker that should tolerate high volumes.
@pengaro yes, icons and text (the whole UI) basically are tailored to the non-XL variant screen resolution, they will look bigger on the XL since that's the scaling value it has been set to. But you can change it with the Ubuntu Touch Tweak Tool.
Thanks for the reply. It's not powering down at all. It literally goes to the Android Recovery screen briefly before the Google splash screen then boots into UT.
For anyone else, if you do a factory reset and wipe out your personal data it will reload the os and work ok. IT would be nice to figure out what app or tweak causes the issue though.