WLAN/NextCloud interaction?

Suddenly, my WLAN connection became unstable: repeated interruptions although the connection still appeared active. Must turn it off and on to repair, only for a couple of minutes (or even seconds) until next interruption.

As the only recent change was my NextCloud account enabled (with auto-sync twice a day), I tried out with NextCloud disabled. Surprisingly, my WLAN connection is now stable again.

Is an undesirable interaction between WLAN and nextcloud plausible? If so, it’s beyond my understanding. I didn’t open a “bug” thread as I’m not sure what really happens.

(Xperia X, SailfishX 3.3.0.16 Rokua without device encryption)