There is an external wiring issue. Do you have any switches or Volume controls in the speaker wiring?

I don’t. Speakers are wired directly to the amp in parallel . Could the speakers have blown when adding the second pair?  Doesn’t seem to make sense?

This will turn out to be something silly. I doubt that the speakers were blown. It would require very high output for a while and I doubt if this would have gone unnoticed. Check your wiring in detail.

Keep an open mind. When troubleshooting once you’ve assumed that the problem must be b...] or cannot be b...], you are likely to be blindsided. But, you should play the percentages. Check the 90% probability before chasing the 1%. I suggest that you follow the speaker wiring, looking for breaks or disconnections. Check every connection. A 0.1% would be that the wires were attacked by a squirrel or racoon.

That really sounds like you have the wire pairs swapped. Make sure the plus and minus wires from each speaker are both attached to the same Amp channel.