Are you able to upload a log bundle from both the SC server and the plug-in server? We can find out where in the process it is having an issue. The SC server side will tell us if there is an issue with most operations, however if there is a problem at the plug-in side the SC server logs will only be able to provide so much detail of the problem.
https://kb.netapp.com/Advice_and_Troubleshooting/Data_Protection_and_Security/SnapCenter/How_to_collect_SnapCenter_logs