When clicking on claims in dynmap, it shows the owner correctly as a player name, but shows UUIDs for those in the trust list.

Same issue here. Running 1.15

There's not been an update to this repo for 5 years so I wouldn't hold your breath for one to fix this issue.

@gjvnq, You may want to try https://github.com/leahshields95/GriefPreventionDynmap.

It's a fork of a re-write but has a number of improvements and runs nicely on 1.15.2, with usernames instead of UUIDs