I ran Ubuntu Touch briefly on a Nexus 5 as well. IIRC the two issues I had were:

1) calls and MMS not working well.

2) Instead of a normal GNU/Linux OS Ubuntu Touch tried really hard to have an Android style immutable OS. Kind of the worst of both worlds since you have a difficult to work with OS but without the app ecosystem of Android that some people believe makes it worth using.

After that I kind of just gave up on the idea that I owned my phone at all and a few years later I gave up carrying smartphones entirely.