You may want to consider installing the milestone build rather than the snapshot. Snapshots can be a little unstable these days while major reorganizations take place.
Did you by chance edit the addons.cfg file (you can find it in the folder “services”)? The original file has all elements commented out, i.e. all lines start with the hash sign “#”. This file can be used for manual configurations, but any entries in this file will overwrite any changes you made in PaperUI, so use either this file OR PaperUI, but not both.
If you did not, you may want to try to Clear the Cache, this sometimes works wonders.