I have an OpenSprinkler DC 3.0, Firmware 2.1.8 in an AVM Fritz!Box 3590 Mesh configuration running. The OpenSprinkler is installed in the Garage and most of the time connected to the WiFI AP FRITZ!Powerline 1240E installed nearby. It is running for months now without any issues. Please be aware that older Fritz!Repeater, like the FRITZ!WLAN Repeater 300 may be part of your problem.