The Original Prusa Printers can manage several tasks simultaneously: this is called multithreading. In case of an issue related to multithreading, the printer will show the message: "Marlin client could not send message to Marlin server and timeout was reached." 

Error name: Marlin Request Timeout

Error code: #26530 (MK4S) #13530 (MK4) #27530 (MK3.9S) #21530 (MK3.9) #28530 (MK3.5S) #23530 (MK3.5) #31530 (CORE One)

Restarting the printer is expected to resolve the error, and this is not expected to occur again. In case a restart does not resolve it, please contact our customer support, and we will take it from here.