ᐅ ERR activates actuator despite being too warm

Hello everyone, and please don’t be too harsh.
Actually, the electric heating resistors (ERRs) have been removed from all rooms except the children’s room.
The thermostat is a rotary type (RTR) from Halmburger, with a scale from 0 to 6.
According to the manual, setting it to level 4 should maintain a temperature of around 20°C (68°F), but in the room it is currently 22°C (72°F), and the actuator is open, so the room is being heated. If I set the room thermostat to level 3, you hear a click and the actuator closes, but shortly after it opens again, even though the room temperature remains just under 22°C (72°F) and the RTR is still set to level 3.

Shouldn’t the RTR only open the actuator again once the temperature in the room drops below, I think, 16°C (61°F) at setting 3 on the RTR?

Or am I making a mistake in my thinking? The temperature is measured directly next to the RTR.

Shouldn’t the RTR cut power to the actuator when the room temperature reaches a certain value? I understand that these analog RTRs aren’t very precise, but a deviation of 6–7°C (11–13°F) seems quite large to me.

Draft present?
How "cold" is the wall where the thermostat is located (is it an exterior wall)?

No, that is not an exterior wall. I would need to measure the temperature on the wall; I should get a device to do that.

There is also no draft. Window closed, door closed.

I can’t help technically, but speaking from personal experience, determining the room temperature is not that straightforward. For example, I bought some Zigbee sensors that are placed on the wall thermostats (at a height of 1.4m (4.6 ft), but directly on the wall). These sensors tend to measure slightly lower temperatures than, for example, a thermostat positioned freely in the room.

Also, a curtain in front of the room thermostats can distort the measurement results.

An IR thermometer is quite useful for this purpose.

I also have several Aquara Zigbee temperature and humidity sensors mounted right next to the RTR on the wall.

The radiator thermostats are basically always bimetallic, and that says it all. The Aqara devices have an accuracy of ±0.3°C (±0.5°F), so their precision is just so-so.