This is as likely an incorrect settings choice by me as it is a bug but all the same...
In the pre-game preview, as per the screenshot below, players are shown in different uniforms and/or caps. This is post a facegen force update (which I don't think has any effect here) and the only fix seems to be to go into the uni settings page and individually update each team each season - a bit of a pain but no dealbreaker.
Still, if anyone has any insights into potential causes I would be most appreciative.
G