If the solution could be moving the saddle forward or back just a tiny bit, then why not try that first? In the recent past, I did rest for weeks, my knees felt better, then I took another few rides and it was back. I don't ride very hard or hammer up hills in high gears. The solution could be something as simple as moving the seat forward/backward 1/8", so why not try that first (after my knees feel better)?
not tryin to be au contrare.
this kind of 'injury', regardless of the origin, tends to flare due to any similar activity; so minor adjustments, which under normal conditions might actually have some real effect, will likely only cause further flareup.
I'm not a bettin guy, but I;d put big money on your tiny saddle move not doing anything except more of the same pain. But then this is the interweb and your idea of 'serious' and my idea of same are bound to be different.
None of us are who we were "Back in the Day". Things we could ride thru and tough over at 30 cause longterm serious consequences for us now. Not to say we can't be strong and move forward positively; we just need to have a much further forward 'view'. I'm no longer "bulletproof and invincible". Twinges in the knee (and currently for me, the left hip) get my attention right quick and make me keenly aware of further progress either towards relief or increased stress and strain. Its the difference between pyschological and physcial. Anytime the 'brain; tells me "I can't", I'm just wimpin. If the body tells me "I can't", I gotta believe.
Since BOTH bikes seem to cause your issue, there is something with both which seems to contribute to the problem, one more than the other. Cycling may not be the only root cause, but it obviously is a main contributor.
I do have to ask, if one bike really greatly increases the issues, why do you persist in riding it on the current 'form'/setup/whatever of the bike which causes the most problem? Don;t make sense to me.
If it's really constant, I'd seek professional health care from someone who understands these injuries.
You note you've had this before, so its never been really defined nor addressed.
Recover, define the problem, start with the 'better' setup machine and refine that until it truly works for you, then match the other machine to those same resolutions.
that's what I'd do... (have done)