The fix provided In JENKINS-75604 seem to have partially fixed the issue but I am still encountering the error (however not as frequent):

"Fail to retrieve the timestamp for tag event <tag>".

I believe the error occur when "type" is "DELETE". As in that case ServerPushEvent is using getFromHash() and thus getting "0000000000000000000000000000000000000000". Using getToHash() might solve the problem. However I have been unable to find how the webhook event for when "type" is "DELETE", so I am not entirely sure.