Having the same problem on Pop OS 20.04 and automatic mounted shares via fstab, and when the stale file handler issue happened, the only change I made was disabling the cache drive for the particular share I was having problems accessing, and it started working immediately without remounting the share, rebooting or even closing Gnome Files on Pop OS. I'll try this share without the cache drive enabled for a bit, and see it works consistently or not.