If more than one variable is used in idvars and one of them has missing values, the code breaks on the following lines:

- if _rc {
  - capture assert !missing(`idvars')
  = capture assert !missing(user_uuid session)
  - if _rc {
  - count if missing(`idvars')
  = count if missing(user_uuid session)

The error I see is

user_uuidsession not found

I think this is because missing() doesn't take multiple variables as input.