The symhelp report indicates two reports recognize some signs that the virus definitions are corrupted. The following article provides some general guidance on how to approach this:
Troubleshoot corrupt definitions in Endpoint Protection
https://support.symantec.com/en_US/article.TECH92043.html
If this is a "one-time" event and correcting corrupt definitons on one system works and allows that system to continue to update, then using that same approach you can correct the issue on additional systems. If new systems are continuing to find themselves in this predicament then it may be necessary to look deeper for a root cause so that it can be avoided.