R7000 in Bridge mode loosing wired clients

Hi all
I have an R7000 which is in Bridge mode and connected to my R7800 in AP mode.
To this R7000 are several wired clients connected, which are most of the day turned off. After 1-3 days, the wired ports stop working on the R7000. The link stays up, but the clients don't anymore get an IP Address from the DHCP server. Unplugging the LAN doesn't help, only restarting the R7000 or sometimes toggling the Wi-Fi off and on. 
I'm running official firmware V1.0.9.42_10.2.44, which is a tad old. But with 1.0.9.60 I had various other 5 GHz problems and had to downgrade again.

Most of the time the R7000 web interface keeps accessible, but not always. When I checked it today, all the directly wired clients disappeared from the "Attached clients" page, while the wireless clients were visible. The attached clients don't get an IP address when the R7000 is in this state.

Is this a known issue?

Thanks
pato