How much data is there in the JSON?
And you are using one of the recent firmwares like 1v97 or later?
1v98 and 1v99
but you say nothing is connected to the flow sensor pins?
A0 pin connected to nowere produced to many "noise" - probably that triggered the problem. Now I connect the real sensor to the pin A0 to make situation close to the real life usage
Is there any chance you could come up with a self-contained example you could send me that actually exhibits the problem?
Well, I'm motivated to identify the problem if it still exists. But for now after your advices probably the solution is found. At least for now the test module works correctly for 1.5 day and I'm planning to use it in real life