After update from jenkins version 2.263 to 2.267 and update of all plugins it seems everything is fine.
But if you change anything in an existing pipeline job, like increasig number of Max # of builds to keep in Discard old builds, and save the changes there, all properties will be deleted.
Just the the configuration of the pipeline stage is there.
I can reproduce this with each propertie in the pipeline job. It affected all general properties and build trigger properties.
There is also a second behaviour. If you change a property in the pipeline script, it is not possible to save the pipeline job.
One of this 2 scenarios will be entered.
After downgrade of jenkins version it is working again. (plugins will not be downgraded)