Your logs show that you have Plex monitoring more folders than Linux can handle by default. (Default maximum = 8192)
Of that 8192, the transcoder needs 2 slots in the monitoring table.
You are seeing partial success because you got lucky (which folders were first created)
Sep 15, 2020 14:45:55.590 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6F96"
Sep 15, 2020 14:45:55.590 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6F9D"
Sep 15, 2020 14:45:55.590 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6F9E"
Sep 15, 2020 14:45:55.590 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FA0"
Sep 15, 2020 14:45:55.590 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FA1"
Sep 15, 2020 14:45:55.590 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FA2"
Sep 15, 2020 14:45:55.590 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FA3"
Sep 15, 2020 14:45:55.590 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FA8"
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FA9"
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FAB"
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FAD"
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] DEBUG - [Notify] Now watching "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FAE"
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FB1" (28: No space left on device)
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FB2" (28: No space left on device)
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FB3" (28: No space left on device)
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FB8" (28: No space left on device)
Sep 15, 2020 14:45:55.591 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FBA" (28: No space left on device)
Sep 15, 2020 14:45:55.592 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FBD" (28: No space left on device)
Sep 15, 2020 14:45:55.592 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FC1" (28: No space left on device)
Sep 15, 2020 14:45:55.592 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FC4" (28: No space left on device)
Sep 15, 2020 14:45:55.592 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FCD" (28: No space left on device)
Sep 15, 2020 14:45:55.592 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FD1" (28: No space left on device)
Sep 15, 2020 14:45:55.592 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FD2" (28: No space left on device)
Sep 15, 2020 14:45:55.592 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FD3" (28: No space left on device)
Sep 15, 2020 14:45:55.592 [0x7f32395d1700] ERROR - [Notify] Failed to add watch for "/volume1/Pictures/Lightroom4Catalog.JeremyS/Lightroom4Catalog.JeremyS Previews.lrdata/6/6FD9" (28: No space left on device)
The solution is to perform this procedure . Don’t forget to allow for extra growth (but not too much) to satisfy your needs because this table is take from main NAS
memory.
Given you estimate some 170,000 folders in use (files don’t matter),
allocating space for 262144 (256K) folders would use 140MB of memory.
If you have 4-8+ GB of main memory then this is of no concern.
