I have narrowed the problem down to the T183 Information Return for Electronic Filing.

There is a new line item under Part C - Electronic Filer Identification.

CRA sent out an email about 2 months ago indicating that they were going to start asking preparers to associate their RepID to the EFILE transmission session...  It looks like this is where it gets input now...  Because there's a new box for RepID where there was none before.  The individual at the EFILE help desk said that for 2022, we could use TEMP001 if we didn't associate a RepID to the EFILER number.

Unfortunately for me... Profile is putting my EFILER number into this box...  I don't know where, under the options panel, to change this.