On geo-fun:
journalctl -u syncthing@vance | grep panic
gives
Jan 10 15:56:14 hal syncthing[20958]: panic: runtime error: slice bounds out of range
Jan 10 16:03:12 hal syncthing[3477]: panic: runtime error: slice bounds out of range
Jan 10 16:31:41 hal syncthing[3926]: panic: runtime error: slice bounds out of range
Jan 10 16:44:52 hal syncthing[5532]: panic: runtime error: slice bounds out of range
Jan 10 16:52:12 hal syncthing[6289]: panic: runtime error: slice bounds out of range
Jan 10 16:57:18 hal syncthing[6743]: panic: runtime error: slice bounds out of range
Jan 10 17:00:44 hal syncthing[7069]: panic: runtime error: slice bounds out of range
Jan 10 17:04:05 hal syncthing[7319]: panic: runtime error: slice bounds out of range
Jan 10 17:06:36 hal syncthing[7552]: panic: runtime error: slice bounds out of range
Jan 10 17:09:46 hal syncthing[7740]: panic: runtime error: slice bounds out of range
Jan 10 17:12:06 hal syncthing[7961]: panic: runtime error: slice bounds out of range
Jan 10 17:14:48 hal syncthing[8143]: panic: runtime error: slice bounds out of range
Jan 10 17:17:02 hal syncthing[8336]: panic: runtime error: slice bounds out of range
Jan 10 17:19:53 hal syncthing[8510]: panic: runtime error: slice bounds out of range
Jan 10 17:22:41 hal syncthing[8715]: panic: runtime error: slice bounds out of range
Jan 10 17:24:59 hal syncthing[8913]: panic: runtime error: slice bounds out of range
Jan 10 17:27:39 hal syncthing[9088]: panic: runtime error: slice bounds out of range
Jan 10 17:30:02 hal syncthing[9281]: panic: runtime error: slice bounds out of range
Jan 10 17:32:18 hal syncthing[9472]: panic: runtime error: slice bounds out of range
Jan 10 17:34:34 hal syncthing[9650]: panic: runtime error: slice bounds out of range
Jan 10 17:36:52 hal syncthing[9820]: panic: runtime error: slice bounds out of range
Jan 10 17:39:09 hal syncthing[9993]: panic: runtime error: slice bounds out of range
Jan 10 17:41:23 hal syncthing[10169]: panic: runtime error: slice bounds out of range
Jan 10 17:44:01 hal syncthing[10339]: panic: runtime error: slice bounds out of range
Jan 10 17:46:16 hal syncthing[10528]: panic: runtime error: slice bounds out of range
Jan 10 17:48:37 hal syncthing[10698]: panic: runtime error: slice bounds out of range
Jan 10 17:51:05 hal syncthing[10875]: panic: runtime error: slice bounds out of range
Jan 10 17:53:37 hal syncthing[11060]: panic: runtime error: slice bounds out of range
Jan 10 17:55:54 hal syncthing[11248]: panic: runtime error: slice bounds out of range
Jan 10 17:58:37 hal syncthing[11420]: panic: runtime error: slice bounds out of range
Jan 10 18:00:57 hal syncthing[11615]: panic: runtime error: slice bounds out of range
Jan 10 18:03:18 hal syncthing[11804]: panic: runtime error: slice bounds out of range
Jan 10 18:05:33 hal syncthing[12181]: panic: runtime error: slice bounds out of range
Jan 10 18:07:52 hal syncthing[12389]: panic: runtime error: slice bounds out of range
I deleted the folder at both ends and created a new folder with a different id, but pointing at the same locations within the file system. This has resolved the issue.
As background, on geo-fun I originally installed the version that is in the Ubuntu 18.04 repositories. I also installed the snap version on dirac. The snap version didn’t have a version id, and geo-fun was complaining about not being able to sync symlinks. So I shut down those versions and installed all from the apt repository.
I thought that I had deleted all of the config and database directories, but maybe I had missed something. I am not sure if this was a contributing factor, but it provides some context in case anyone else is having problems.