There is a timing issue when updating a parameter that is referenced by a running processor. Updating the parameter context stops the processor and tries to restart it. However, validation of the processor might not be complete by the time it is attempted to be restarted and you can get an error (see attached image) and the processor does not restart automatically.
Steps to reproduce:
1) Create a process group with a ListFile and LogAttribute processor .
2) Have the input dir be a parameter on the ListFile. Set the parameter on the PG.
3) Have that running. Then go change the parameter value on the PG level. It will auto-restart for you but fail because validation wasn't done yet for ListFIle resulting in a now not running processor.