Very interesting. I wonder if over time you’d developed a colony of stinky bacteria that were immune to the ingredients in your particular liquid detergent. Which were duly slaughtered by the new different pods.
If you still have any of the old stuff, it’d be interesting to switch back to it for a few weeks and see if the issue recurs. And if it does, see if a different liquid detergent solves the problem just as effectively as did your new pods. Science!
Waay back when I used loose powder detergent. I’ve also used the goopy liquids, but it’s also been a long time ago. For the last ~20 years I’ve used the hard pelletized powders or the powder sachets encased in dissolving plastic. Now my new wife prefers the liquid-filled pods, so that’s what I/we use now. Never had any persistent odor issue no matter what form of detergent I used.