Most of this stuff sort of sprung up in my head during a conversation with Mr.Meowth on Discord, whose forum name I don't know so I shall have to tag him properly once I've found out!
Once I stopped thinking of the glitchiness and "infiltration" anagram as hacking, I started thinking, again, about what they might mean. Specifically Infiltration.
The glitching stuff has been going on for a couple days so I've been able to think about that, and I kept thinking back to Ana's "memory recovery" in the Missing Children quest, Code: Angelus' "CORRUPTED DATA" Rift Notes, and our own "memory glitching" in Hiyoshi (although given our proximity to Ana's grave/likely old house, I wasn't sure how much of that was actually us and how much of it was a flashback/cutaway.) And then "Infiltration" happened and I realized that instead of referring to simply an untrustworthy person in a group (as was my very first theory upon seeing the word), it could be more of a mental or spiritual thing, and that something is or has infiltrated people's minds. And then I realized that that's essentially what we do, whenever we see from someone else's POV or play as another character. And I started wondering if that's what the Interceptor really is, as was already more or less implied by the Puppet Master.
And suddenly Nymiera's certainty that we, or our character, are someone named "Adrest", and our character's reaction without our input, made a lot more sense.
Then the green text on Zumi's post happened. "You thought you got rid of the problem and that I was gone? That's cute." And the renaming of the item thread, "Commence Deletion". Which, clearly we aren't doing. So it begs the question of if we're not the only ones doing the "infiltrating". And "infiltrator" sounds awfully similar to "interceptor"...
So basically my theories amount to this: The "repressed memories" we have that basically knock us out in Hiyoshi are basically past incarnations, timelines, or "runs", the same way Ana had some sort of past incarnation before. And the "infiltration" is being done by some sort of counterpart to the Interceptor, likely related/connected in some capacity to Indriad. (Especially given Indriad's Arceus cult, the way anything related to Arceus gets glitchy in Reborn, and how in the two locations most connected to glitchiness- Hiyoshi City and Dylan's house with that cliffhanger with Ana- both have symbols of the Reborn Gate behind which Arceus' meteor is supposed to be. Ana even says she "gets a bad feeling" from that symbol.) Madame X knows the Infiltrator is a thing, which is possibly why she isn't overly concerned about the interceptor's turning up. And possibly, in the past, the Infiltrator was, or was "watching", Erin, and that's why the twins recognized her as 'Eriena.'
(Given the ending of v11? My prime candidate is Amanda. But I really don't have enough to go on for that one.)