How can I force .stignore to be applied?

I have a bunch of files that are stuck in the synchronization because they are in use:

AppData\Local\Packages\5319275A.WhatsAppDesktop_cv1g1gvanyjgm\LocalState\applog.txt

hashing: open \\?\C:\Users\yop\AppData\Local\Packages\5319275A.WhatsAppDesktop_cv1g1gvanyjgm\LocalState\applog.txt: The process cannot access the file because it is being used by another process.

I do not care about these files and I added AppData to .stignore (by going via Folders → my folder → Reduced by ignore patterns).

This however did not close the problem, as if .stignore was not re-read. I tried to force resync, pause and restart the synchronization for this folder but the list stays as it.

Adding the folder to ignore patterns should be enough. Can you post the actual content of your ignore patterns?

Thank you for your reply. As I was about to get the content of .stignore I realized that it has now been taken into account.

There seems to be a delay of some sort, longer than about 15 minutes (which is approximately the time I was fighting with the problems)