I've figured it out.
In case someone runs into the same issue, you have to edit and save those actions that will cause errors. It will regenerate the XML correctly.
Seems like in the past you were able to choose a column for the user or group attribute and it would remain saved in ACT_Configuration column.
Currently saving over the action removes the "<tocolumn>Login</tocolumn>" field, replacing it with "<tocolumn />" that the current version works with.
A simple sql to start with: SELECT * FROM WFActions WHERE ACT_ActionKindID=13 AND ACT_Configuration LIKE '%<TO%COLUMN>%'
I haven't tested it, but I assume It'll result in an error as well for DW (CC) and UDW (BCC). If not, then instead of '%<TO%COLUMN>%', use '%<TOCOLUMN>%'.