I have one clock (V49) which has frozen after around 50 days. Can't say the exact number of days but it's close to 50. It's done it twice now (in about 100 days), so there seems to be a pattern.
After a restart it's ok again.
Hmm, I don't know how that could be. Things in V49 are done in a totally different way, and there should be no effect on rollover. Let me break out the instrumented version of the code again and have another look at it.
I see new code for ATMEGA328 and ESP8266 are avaliable.
It seems to work fine with both RTC and ESP8266 in parallell.
Care to elaborate on the changes made and the relation between RTC and WiFi module?