Random elements appearing in rendered export that aren't in the Timeline

I created a text reveal in Particular (in a few nested comps) within my main composition. The Master comp is a 4 minute long animation, and this text piece is about 9 seconds towards the end. Everything looked clean while scrubbing thru the timeline, as well as in a RAM preview. But when I export it in Media Encoder (my usual method) OR within AE, random pieces of that text are popping in and out of my entire Master comp for 1-6 frames, every second or so. I've been using AE for over a decade and I don't recall this ever happening like this.

My troubleshooting has included exporting out just the alpha'd Particular piece, and replacing the Particular comp with that. Then clearing out all caches, deleting the previous AME folders, reducing project so that Particular comp isn't even in the project anymore, and restarting AE and the computer. There's no indication of a problem until I export. Then that stupid text is popping in and out again. Interesting point of interest that may be a clue, these artifacts seem to always happen in the same places in the export. I've also tried exporting in different codecs, such as JPG sequence, ProRez LT, and Animation.

How do I fix something I can't even see or find in the timeline? These glitches only appear in the exports.

Thank you in advance for any advice or help!

(Some specs: I'm running AE CC 2019 on a Mac 10.12.6)

-Lauren