Wifi clients are not accessible from other wifi clients after some time

I am Using a Xiaomi 3Pro with Openwrt. The Wifi Chip is a mt7615.

edit: other wifi clients are also affected (amazon FireTV and iPhone).

After about one day of usage my AirPrint Printer and Bose soundtouch Speaker are no longer visible on my Macbook and my ios devices (for the soundtouch I use the Bose app). Both the printer and the speaker are still connected to the wifi (at least the luci wireless page states that). After I rebooted the router, both things work again for the next couple of hours. I think it has something to do with the wifi, as using the closed source drivers (MTK with the same version of OpenWrt) does not lead to that kind of weird disconnection issues after some time.

the issue happens at least with the last master builds and 19.07.X

Any ideas what can cause the problems or is there anything I could do to help debugging it?

Start by reproducing the delayed loss of visibility among Wi-Fi clients on the Xiaomi 3Pro with the mt7615 driver, comparing behavior across the reported OpenWrt versions and the closed-source driver. No source file or test is named; collect relevant driver and network logs before narrowing the failure. Done means identifying the cause and validating a fix against the printer, speaker, and other affected clients.