How Bosch front-load washers are put together
A Bosch washer seals the drum behind a locking door, fills with a relatively small amount of water, and relies on a drain pump to empty rather than gravity. The door must lock before the cycle will begin, and it stays locked until the machine is satisfied the drum is empty and stationary.
That sequence explains a lot of Bosch symptoms. If the door will not lock, the cycle never starts. If the machine cannot confirm it has drained, the door will not release at the end.