Grade Step Progression produces invalid Errors on UI but not in Logs, sometimes

Summary:

Each month we process Grade Step Progressions and each month we receive Errors on the UI that are not valid. Reviewing the log shows no error and that all criteria for progression are met.

Content (please ensure you mask any confidential information):

We try to replicate the error in our non prods using the same parameters as Prod, unfortunately normally a day or two after our users have reported it but there are no errors on the UI in our non prods, indicating perhaps that Sysdate is impacting the results. Has anyone else encountered this? It's a nightmare to replicate cause identical scenarios produce successful results. We have had an SR open since June 2023 trying to resolve. Everyone who looks at it focuses on Fast Formulas but these work so I'm really keen to understand if there's anyone