Measure your heater resistance of the heater in the heater block. Approximate heater resistances are 4.8 Ω for 12 V 30 W and 3.6 Ω for 12 V 40 W. See Proper hotend heater for Reprap x400 Pro V3
Note: you could have a heater measuring the correct resistance but have a poor connection in one of the connectors.
This has nothing to do with OctoPrint itself, the cause is related to the printer itself, not the print server running the printer.
This is a pretty commonly seen issue (usually seen at heated beds), this is caused by faulty wires/cables or connectors. This usually happens after a vast period of usage. You should (periodically) check the cables and ...