I experienced a startup crash with paucal 0.4.4 just now on Forge. Enclosed is the log in question; it didn't get far enough to provide a conventional crash report.
latest.log
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Ah yeah no wonder, the refmap isn't making it into the jar somehow.

Hey, can you upload that to a service like pastebin or github gist, please?

Whoops yeah someone else is having the same issue. I'm working on it ...

Apparently it's a rare but well-known issue with forgegradle no one knows how to fix other than rebuild the jar manually. I've released a version 0.4.5 that should be validated by CF soon; it should be a drop-in replacement for 0.4.4.