I added the regex expression and pressed Update which resulted in the first two calls (662).
After a few seconds the 760 calls dropped which resulted in the regex area being minimized again.
When I opened the regex area again, the expression was gone, but when I clicked Update again, the regex was still present in the transformation as you can see on the image above
With large dictionaries, such as https://app.elexifier.elex.is/dictionaries/xml/760/transformations/662/, the regex value dissapears from the interface, but it is still present in the call. See image:
What happened here was: