I would start with sk101878. Hopefully, your cluster already has CPView History enabled. Without history enabled, you won't be able to go back in time and see what happened.
cpview history stat will show you whether the feature is enabled. If it is, you should be able to scroll back through the CPView data. If it isn't, cpview history on will enable the feature. Unfortunately, you'll be stuck waiting to see if it happens again if it wasn't turned on.
Once you establish whether it is enabled or not, I'd check out the CPView User Guide. For some reason, I can only find one designated for R77.20. I don't know if there is a newer guide out there somewhere that I'm just not finding? Regardless, the guide should give you a pretty good explanation on how to use the tool to extract the information you're looking for.
Good luck!
R80 CCSA / CCSE