super strange amp/cab issues

[niksureal]

so my wife and i are in a band together, we have been sharing a single speaker cabinet for years. one jack is wired to one of the speakers and one jack, the other. we like the lack of sonic separation and lugging less shit around doesnt offend us. there have been zero issues all this time. until today!

i turned the power strip that has our pedals plugged in on and her amp on while i finish setting stuff up (just like always).
when i turn my amp on though, her bass gets twice as loud and also starts coming out of my speaker. literally nothing has changed in the past 50 times we've used this setup but this is the first time this has ever happened.

the only thing we share in the entirety of the signal path is the metal plate that i assume grounds the jacks together, in the speaker cab. so i assume this has something to do with it. but why the sudden change?

i tried plugging our amps into opposite cab jacks, different power jacks, swapping power cables, switching power jacks for our pedals, different guitars, checked the jacks in the cab and speakers to see if contacts were touching something not ideal or if wires had come undone or been clipped to speakers wrong. nothing appears wrong or different, nothing i did improved anything. i even flipped the speaker cables to see if there were any directional preference and flipped ground lifts etc.

am i right in assuming its the ground somehow?
should i get another jack plate so there is absolutely no common factor in our setup?
i am at a total loss and getting super frustrated.

[oid]

perhaps a different speaker cable got use this time? One that has ground and hot reversed on one end? I am not sure if that could cause it though, my head is not happy at this moment.

Sharing the ground should not matter since if the amps are plugged into the same circuit they already share a ground, but I can not draw a conclusion as to the effects of a miswired speaker cable at this time,

What are the amps in question?

[niksureal]

quilter 101 and trace elliot elf are the amps. i did switch cables and which end was plugged in etc and had no improvement.

edit: just took the back plate off and took a real close look. one of the jacks is extremely corroded. if the ground on that jack wasnt making contact anymore, could that cause this issue?

[oid]

That is a puzzle. The only reason an amplifier output has a ground is if one of the connections is connected to ground in the amp, otherwise they float and have a negative and a positive. If either amp has a plastic speaker jack or a metal jack with plastic isolation washers that could mean it is floating, and I just can not sort out how the amps would interact in such a case, my brain is missing something big, but I just can not quite make connection.

If the speaker cables are the same two you have always used in the past it suggests something changed in one of the amps and it did not like sharing that common with the other amp. No idea if this will be an issue in the long run, I am not familiar enough with either of those amps to say. It would be a good idea to separate the jacks onto their own plates or use a non-conductive plate.

I would unplug your amp from the cab and see if your wife's amp still comes through both speakers, if so you know it is something with the cab that you just missed, if not that suggests the amps were interacting with each other through the jack plate.

EDIT: that is assuming you do not have any switching jack fun setup in the cab so you can still use it as a 2xX or 2 1xXs, if you have such an arrangement you will need to make accommodations for the switching for the above test to tell you anything.

[niksureal]

i replaced both jacks in the cabinet, still using the same overall setup as always and now it works fine. i guess just the jacks were corroded enough to create the issue. sheesh. still doesnt seem like it would create that type of problem. seems so weird. very confused.