Android client looses wifi connection after 12 hours

Hi,

My Pixel 3 with the latest Android 11 image looses the wifi connection to my TP-Link Archer C7 v2 (OpenWrt 19.07.6 r11278-8055e38794) after exactly 12 hours sometimes.
The system log says "IEEE 802.11: deauthenticated due to inactivity".

It happens also when I had used another wifi in the meantime.
Means when I stand up I switch on my phones wifi. It connects to my privat wifi e.g. at 7:00am. I go to work, use the company wifi there, and when I go back to home the phone looses the connection to my privat wifi at exactly 7:00pm, even when I'm currently using the connection for a VoIP call or something else.

According to my logs it seems that it only happens when the first connection 12 hours ago was established to the 5G wifi (I'm using the same SSID for 2,4 and 5G wifi).

I've already found the FAQ article how I can disable this "inactivity timer" (https://openwrt.org/faq/deauthenticated_due_to_inactivity).
But this refers to an issue due to the energy optimizing mechanismen of Android/iOS, which deauthenticates the connection after the device enteres the deep-sleep.

I will try the mentioned setting for the wifi interfaces. But I'm wondering if someone can explain this behaviour or has the same issue.

Thank you.
Jas