Maybe the update reverted some settings or your library just grown to big? You can use a search engine of your choice, searching for “Synology inotify”. Use information found by that search to check the relevant settings on your NAS. What are your current settings? How do they fare in comparison to the total number of files and folders in the folder watched by Roon.
Update:
Checking that this “The user account must be allowed to raise their ulimit -n value to 8192.” (from Installing Roon on Linux) is (still) true might also be worthwhile.