Greetings all.
For those who use Explicit GUP policies, please keep a look out for what we initially believed was a bug in the RU5 SEPM, but after since discovering it at a customer who is isolated and soley using RU4MP1 for both SEPM and SEP Agents, we believe that this issue may be a "time-bomb" defect of sorts, i.e. after a specific period of time this issue begins to occur. This is just a preliminary theory.
Some SEP Agents (no pattenr as yet) and their Explicit GUP policies are randomly going haywire on the SEP Agents' end, and there is no fix that we can tell. We reboot the system, or cycle the SEP Agent services which seems to temporarily fix it, but very soon after it starts all over again. Just ongoing lines of "Using Group Update Provider type: Mapped Group Update Providers" and it does nothing, it stops updating VirusDefs. Oddly other components appear to still be updating. IPS, Revocation Data etc.
Note that we have made NO changes to our GUP policies or Location logic that have worked perforectly find for all releases of SEP 12.1. It's remained the same since RU2, RU4, and RU4MP1.
Our SEP Agents for all affected customers still contain a mix of RU2, RU4, and RU4MP1