If [return_type] is omitted then ist always evaluates to #VALUE error. But even if you set [return_type] then it evaluates not always correct. See https://stackoverflow.com/questions/69388863/formula-cell-does-not-get-evaluated-until-formula-is-focussed-and-confirmed-in-e/69390917?noredirect=1#69388863 for a complete example to reproduce the issue.
I've added a few commits to try to improve things - main one is r1893852