They are the same boiler, the same piping, the same water, and the same pressure.
The first ones are with clean water. Notice the light, fluffy steam, with NO water carried with it. The steam vapor RISES into the system.
The others have a tablespoon of cooking oil added to the boiler water. That's the ONLY difference. This is what I think is bringing back the crud.
The next ones are with the oily water.