I’ve been seeing this problem about being unable to ssh in or contact the app via mobile or (old) web interfaces for quite some time (most of the summer). It will run about 1 week, maybe 2, and then this problem manifests. I have to reboot the OSPi to get back to normal.
I’ve tried updating the rpi OS (operating system, not Open Sprinkler) multiple times via apt-get update/upgrade but this hasn’t changed behavior.
I feel vindicated that another user is finally reporting this issue. Are you running longer term tests on older boards with older firmware?