Hotend thermistor/heater degradation?

This is something new that I was surprised to experience.
I have a Rapido on my V-MiniON, and I used to print PETG with no problem at 230 degrees.

Recently (starting yesterday, actually), I started to print something and ecperienced all tell-tales of "hotend too cold". Reported temperature was 235 degrees Celsius, +/- 0.1 degrees, but as soon as printing speed started to exceed a measly 50 mm/s, the material became opaque, layer adhesion became crap, etc.

Same filament, same spool, same model, same settings, etc., etc.

Could the thermistor have degraded for reasons unknown?
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