What version of Acumatica are they on? We found this on early versions of 22R2 believe this was the issue below it disappeared once we updated them to a later version
AC-257592: After several switches between different forms on the same browser tab, if a user was trying to execute an action or to save an entity, an error about a required box being empty could occur, for example: Inserting âBilling Addressâ record raised at least one error. Please review the errors. Error: âRevision IDâ cannot be empty. The error could occur on different forms, such as Sales Orders (SO301000), Shipments (SO302000), or Purchase Orders (PO301000).
Workaround: Please find the solution in this knowledge base article.