The Original Prusa MK3.5 continuously monitors the temperature of the tool head in use and its variation with respect to an expected reference. In case the printer recognizes a variation out of the acceptable range, it will display the following message: "Measured temperature is not matching expected value. Check if the thermistor is in contact with the heaterblock. In case of damage, replace it".
Error name: Hotend temp not matching
Error code: #23210
In this case, the printer will stop the heating and display the message on the screen. The printer then waits for the user to inspect all parts and fix the issue.
If the issue persists, the error likely stemmed from an issue with the hotend thermistor or, more rarely, hotend heater.