It's a 2003 Honda Civic EX with 263k miles

I've read a lot of forms about this but I feel like mine is slightly different.

Started with my alternator going out and I went to AutoZone and got a remanufactured alternator, put it in and started up everything was working fine. on my way to work the next day the batteryight was flashing but I just had to trek on. On my way home battery light was solid and made it about one light before everything just died. Pulled into the lot and realized I forgot to tighten the tension both and my belt was completely off. Had my SO run me some tools and got it all buttoned up and started the car. Battery light was still on solid and check engine light flashing, after a few flashes it stayed on solid, battery light went away, and the car was in limp mode with the tac showing 0 and the coolant temp dropping to nothing. Limped to AutoZone and OBD read no connection, every time I turned the car off and back on this cycle repeated.

Fast forward the next day I left the battery disconnected over night plugged it back in before going to work and battery light was on solid but it wasn't in limp mode. I drove it for several days no problems and then the limp mode started again. After reading some forms i realized the ground still might not be good and when I popped the hood the top alternator bolt was actively arcing, I shut everything down took everything back apart and added a "failsafe" ground to the bottom alternator adjustment bolt and ran it to the battery. This again stopped the limp mode issue for a couple days but the battery light was still on.

ive now started to have the limp mode issue again so i decided to double check everything all my bolts are tight and grounding cable is still attached so I started to tear into the dash to get my ECU. Pulled it out and took it apart but I don't see any burnt chips or shorts everything looks normal.

I'm not understanding why sometimes it goes into limp mode and sometimes it will work fine for days. I feel like if my ECU was truly fried it would be a constant issue not intermittent. And before I go spending money I want to make sure it is truly the ECU and not something wrong with the remanufactured alternator that failed. &/Or before I go buying a new ECU I want to make sure the main cause is truly fixed so I don't potentially mess any replacement parts up.

For reference my top alternator bolt is stripped and is held in with a nut rather than screwed into the bracket if that makes a difference.