Temperature gauge intermittent

From cold start temp gauge works.

When the engine gets to about 90DegC, the fan kicks in but occasionally the temperature gauge goes back to the cold position. The MFA oil temp reads 100+DegC

Happens a lot when stuck in traffic or when the engine is very hot.

When the car starts to move (no more traffic), the engine cools down with the air flow and the temp gauge starts to work again and MFA oil temp goes to about 90DegC.

Car has overheated recently, need to sort this out but I don't know if the car will overheat when stuck in traffic because temp gauge stops working when very hot.

Nowadays sitting in traffic with heater set to full heat and max blower to stop car from overheating.

Dodgey temperature sender? Wiring issue?
 

the temp sensor is the black one in the front or side flange, make sure its clean and the wire connection is clean and tight, repalce the spade if its dodgy. chase the wire back looking for damage, but by the sounds of it you need a new sensor