Our roller garage door misbehaved recently closing fully and then partially opening up by a few inches. Turned out it was a feature of the sensor that detects when it is fully closed. The sensor is a small battery operated circuit that is linked to a pressure sensor in the rubber seal on the bottom edge of the door and communicates with the main control unit by radio. When the batteries start to fail the behaviour mentioned in the opening sentence happens, changed the batteries and all is normal again.

Mind you getting the batteries was one issue and their price eye watering.

https://www.amazon.co.uk/EEMB-ER1450.../dp/B074QMH2DZ

Richard