Has anyone seen/resolved the following error when trying to save a sales invoice using SalesInvoice.Save()?

Error: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index

It worked fine before we switched over to version 2021.1.1.176. I run validate on the SalesInvoice and get no errors, but as soon as I save, I see the error above.

Additional info: I have also noticed that the EmployeeFactory.List() seems to return that error whenever I try to do anything with it. I was trying to go through the employees to find a sales rep to assign to my sales invoice and I get the same error. That is something I did not do in the past/before I started to troubleshoot this.