To give you a little background on what's going on...
I mod 2 different subs, with users who are members of both.
In SUB-A, 2 users got into a personal spat with each other about a month ago, and are now adversaries.
In SUB-B, these same 2 users were having a discussion about something, and the comments eventually devolved into back-and-forth of "I'm right, you're wrong" and "no, u" snarkiness. USER1 was warned to stop stirring the pot, and to not target/harass others. USER2 was advised to block and not engage further, as USER1 had shown the conversation was no longer in good faith.
Back to SUB-A.
USER2 and unrelated USER3 were having a conversation a few days ago, which included reference to an unnamed user that they both don't particularly like or agree with. Their comments were both reported today.
The reports were freeform text, said USER2 and USER3 were lying and/or biased about the unnamed user, and referred to being personally warned in SUB-B unfairly. Making it very obvious it was USER1 doing the reporting.
What's the best course of action us mods should take in this area? Do we warn USER2 and USER3 to take commentary about other users to PMs? Do we warn USER1 not to use the report feature for personal issues and complaints about other subs? Both, neither, something else?