That's super irritating, sorry you're still dealing with it.

I'm thinking long shot items now;

I realise I've been focusing on the heat itself, but could your extruder be skipping? There's no grinding or dust in the gears? In really bad cases they can chew into the filament itself, I've had it happen moreso after clearing a clog but it still can happen, cleaning it with air and lightly oiling the gear mesh is a decent start.

Don't think it's related but might be worth dropping your klipper configs, specifically around hotend stuff.

Have you tried totally new nozzles? Could have a very slight partial clog remaining that keeps showing up.

Do your part cooling fans blow directly on the block? 4th layer is about when that would kick in for my config with PLA, I have socks on mine and I run stealthburner hotends on both my voron and prusa so they blow below the block, but even then you can notice and definite change in cooling rate of a hot block.

I know I brought up intermittent breaks before, klipper by default looks to do 1s input smoothing on the thermistor to reduce sensor noise which could maybe hide it, but that's unlikely, I've seen it on my printers
this was on the prusa when it was running marlin still, very obvious at this point but it was having clogging and printing issues before it started to trip thermal runaway.

What sort of print speeds are you doing and do you happen to know the material your block is made of? 200 is cold to me for PLA, while I know its smack in the middle of a lot of manufacturers, personally run closer to 215, prusament's profiles are 210 if I recall. Not something that's going to suddenly cause you an issue though, only thought I could have is same temps with higher speeds/feedrates

Might be worth doing a cold pull to thoroughly clean the nozzle which prusa suggests pla works best for, or run cleaning filament through if you have it. i swear it's just hot glue in filament form but man if it doesnt actually clean things up nicely when I use it for material changes.

Other thoughts, is your PID tune not aggressive enough? I've found that klipper will do its best to hit a target temp with minimal overshoot where marlin would run to a temperature, overshoot and then try to maintain it, if you've change anything in your setup at all I'd suggest retuning it with fans running at your regular fan speed, I do 250 at 50% as that's around what I'll use for abs and petg. Filament super dry? While wet filament can cause a bunch of other issues with print quality, I could totally see it contributing to clogging as well.