So yesterday my WiFi router had a problem and I rebooted it. Strangely enough, now I cannot observe any lost-connetion issue on any of the test units. I have three test units, two OS 3.2 (running 2.1.9(3) and 2.1.9(4) respectively), one OS 2.3 (running 2.1.9(4)). On each unit I set a program that runs a zone for 1 minute and repeats every 10 minutes throughout the day. I also use IFTTT to send notifications to my email upon program start. All three units have been running fine so far (more than a day) and all notifications were successfully received. So, the issue has become more elusive than ever since now I cannot reproduce it. Given that I rebooted my router, I suspect the router may have had a DNS problem causing timeout which then led to issues on OpenSprinkler. In any case, I don’t have means to debug the issue right now since I cannot reproduce it. But I will continue to explore the W5500 route as I am expecting the adapter PCB to arrive in a day or two.