Hi. I believe this started after the last PL9 update (9.1.1 build 26). When I export a file to PS to do editing and then save the image in PS usually the file will be sent back to PL with the changes reflected as a .TIFF. Since the last software update, it appears the update .TIFF is not showing up unless I actually close PL9 and then open it back up.
Hmmm, running PL9.1.0_488 (Win) immediately updated the library and filmstrip when I added (raw) files using a file manager. – However, the OP is on Mac.
I just tried this and was able to bring this subdirectory “to light.” But sometimes you have to click on a different folder and then return to refresh the LHS list.
On macOS the system handles that all by itself in the background.
If you are in an app - let’s say a ftp transfer app - and you need to refresh the external server resources. You would do a standard cmd-r for reload or refresh.