There was an error in an expression in Process Model Properties at Process Start Form : Variable(s) not found: ri!cancel

hi...

i have deleted an ri-variable in a form.

I then go to the process that has the form as the start form - delete the interface and select it again as the interface.
The deleted variable is no longer visible as an input variable.
It has also disappeared from the process variables.
If I want to save the process, I still get the error message:

There was an error in an expression in Process Model Properties at Process Start Form : Variable(s) not found: ri!cancel

before:

after:

What can I do here?
Where else can I delete the variable?