Ive installed ut on nexus 5 several times each phone is different. My tips would be to start with android rom with twrp. Unlocked then use ubports. I use it from snap. But also restarting ur computer. On my nexus 7 i had to be in su on ubports even tho its not recommended. Lol id try alot. Restart, reflash android, use snap package, try several times sometimes it works the fourth time. Also when you do install it and its in the ubunti touch logo it usually stays there for quite some time, pretty sure its still installing. Let it sit there for like 20 min on charger.
Thats all i got. I do know u can do manual install but havent had todo that yet