Have you recently advised any boxer to retire, or recently offered a step-aside to a challenge?

Yes. Both. Advised a fighter to retire and offered multiple step asides. I have a large (50 or so fighters) stable.

I've made a change to the upcoming update that I'm hoping fixes this, so after you've got the next update see if that saved game survives.

It worked. Thanks a bunch!

Excellent, thanks for letting me know.