The best solution in an env like this would be to have a good APM like AppDynamics. If you don’t have that and can’t get it installed, next best would be good l

The best solution in an env like this would be to have a good APM like AppDynamics. If you don’t have that and can’t get it installed, next best would be good logs and a good log aggregator/search tool like splunk. Another option (sorry in advance, this sucks, but “works” to find these issues for some definition of “works”): Branch off the last good version, apply changes one by one (or bisect) and push them out to one of the complaining customers - hopefully with their collaboration. When it breaks again, you know where to start looking. Good luck!