It can be very common in your machine, especially if the rims fall onto the rail with high speed and hit the rim support heavily, causing a loose screw. Pay attention to whether the sensor that detects the rims on the entry rail was activated when the rim was in the correct position. Once the rim enters the machine, the sensor should be deactivated.
If the sensor still detects a rim on the rail, whether because there is actually a rim on the rail or due to a malfunction, the machine will not start the process until the rim or the issue causing the machine to believe there is still a rim stuck in the same position is resolved. Please refer to the example video for further clarification.
Just check if there is something blocking the small metal plate on the entry sensor or if there is something in front of the sensor that is causing the machine to incorrectly detect that a rim is still stuck at the machine's entrance.