Uh, what was it?

Combination of things all brought on by a broken shock. Not a mount. Broken somehow inside. Locked up tighter than a drum.
First thing I did was pull the bag and stick a fingernail in the air valves. Front had air back had none.
That they leak is no surprise. They all do. But it had just been checked and filled ten days ago. And I've had the Showas run flat on me before and they didn't ride like this. So knew there was more going on. Was at least pretty confident whatever it was in the rear though.
Wiped the swingarm down to begin to visualize and grope everything and noticed it just didn't look right. It was torsionally flexed. Not a lot. Just a small amount actually. But it was there.
Thought bushings had given up and whole thing had moved. But they appeared ok under visual inspection. Was changing shocks anyway so took the old ones off.
Popped off the right one and the swing arm went "thwunnnng" and everything fell back in to alignment (at least visually). Took the other end of the shock off then "studied" (i.e, shook the chit out of it and boinked it against the floor) it. It failed the rattle test. Fiddled a little more and the shock she don't shock at all.
So one side was trying to work and was no doubt flexing a little while the other side was a solid mount. Sort of a semi rigid.
The Progressives went on. Still studied the swingarm very very carefully. Some later rainy Saturday I'll pull the back end apart and make sure the swingarm is flat and untweaked and that the bushings and cleve blocks weren't hurt by whatever stresses they might have been under. It had to suck back there when a new longitudinal axis was being created for them to try to rotate around that they simply couldn't rotate around.
With the shocks on, however, it rides great. Significantly better than with the Showas before they broke. Perhaps the bike knew the Progressives were in the garage and this was its way of telling me to install them.
Summary would be 45 minutes of shock install and close inspection and she seems fine again. More follow up will happen later. But I'm not too concerned. Thank goodness it rides right again.