"Exception in expression" error during Autocomplete Rules trigger

Summary: We have an Autocomplete rule which should trigger error message when trying to perform Domestic legal entity change or Transfer of an US employee on any date besides 1st or 16th. While trying to replicate the scenario in redwood create/edit offer Page, we have 2 observations:

A. The error does not pop up upon clicking "Continue" button on the basic info page. (Which is a different experience than RUI pages)

B. It pops up the error message upon clicking submit but does not show the actual error message. However, shows some "Exception in Expression" error

Snippet of the error message & Autocomplete rule attached below: