The function 'isnullorempty_appian_internal' is unavailable

Could you share your code please?

If you're using a!isNullOrEmpty() in a Rule node (and potentially other places in process models concerning decision logic, like timer conditions), unfortunately this is a known issue that I reported to Appian a few years ago and still hasn't been addressed.

Could you please confirm if the below rule in the timer is causing the error?

 if(fn!isnull(ri!array),true(),length(ri!array)=0)

I think you'll be looking for a place where you've used the newer function a!isNullOrEmpty() (and maybe alternately a!isNotNullOrEmpty()).  Your error message (as far as i've seen) has to do specifically with these newer functions.  The code you've posted here using older functions should not be causing any such error that I know of.

(BTW: Stylistically, we don't usually usually use the "fn!" prefix in front of legacy functions, outside of being called by looping functions anyway, though AFAIK it shouldn't break anything like seen in your original error message.)

a!isNullOrEmpty(pv!reassignUser)  this was the code used in the failed instance in the timer.

yes, that would do it.  you'll need to replace that with the primitive function "isnull()" unfortunately.  at least, until Appian fixes this bug.

Great, thanks for the help :)