Canadian Payroll Update 7.3H - Unable to convert data in PREMTF table

I'm getting the above error when updating a client payroll database from 7.3F to 7.3H. The Sage 300 system is 2018 PU7. Payroll subscription is current.

I've seen this about 5 years ago but not since. Can't for the life of me remember what the solution was.