Windows desktop client Sync folders that didn't change

Hi there,

I’m requesting help from you. whant to know why sometimes, Desktop client think it needs to synchronize all my folders (even if both pc folders & nextcloud replication folders are same).

I have my pics on a special folder on my pc, i back up it on a nextcloud on my rpi4 (in my local network).
Don’t nextcloud use hashes to know if something had to be synchronize ? if so, why it restart synchronisation sometimes ?

My PC is win7, Desktop client is last version from now (3.1.1), my nextcloud serv is on raspberry pi 4, last stable version (20.0.4).

I use external disk on my nextcloud to save the files, maybe it’s the problem ?

Do someone know how Desktop client verify if a folder need to be synchronize ?