I guess I will take another more drastical route for this problem.
I don’t think our problem is wifi related, at least not related to our home network.
But I don’t really have the time to start investigating in the Arduino code.
I am logging my weather station data with several methods into Home Assistant and InfluxDB. I can also reach the data from Node-Red.
My best idea at the moment is to revert to manually setting the watering percentage and this will be done regularly over the API from Node-Red.
Maybe I can use the output of the original weather service or simply recreate average values via InlfuxDB queries and override them in case of rain.
I already have a Node-Red flow that calculates the percentage every 30 minute from data from the OS and the weather service for display.
I hope I will be able to find the possibility to change watering level within the API documentation.
It is strange, that only we two are having this kind of problem and as long it is not getting reported by many users, there is no change to get it solved.
You already came a long way with your investigation.