What gameplay feature is this bug affecting?
Reverse breeding

What's the issue? Please include any error messages you receive and as much detail as possible.
I had someone reverse breed to one of my lionesses (paid fee & had the required items for using the internal reverse breeding system). However, on the day their cubs were due, I got a message saying the litter had been lost from the lioness not being nested (shouldn't be possible since a reverse breeding requires besting material to be accepted in the first place).

It was user #49900 who lost their fees, items, & cubs, but since I got the message on my end I figured it was best if I reported it. Thanks so much for any help with this!

Any links relating to this bug? For example, if a particular lion is bugging, what is the link to that lion?
https://www.lioden.com/lion.php?id=794150842003

Any screenshots you can provide us with?
Screenshot of the rollover message: https://i.ibb.co/DzN64yj/AFDF3934-A0-D4-41-CF-93-C6-9-EB6-E4-C1-EADC.jpg

Please provide us with step by step explanation how this bug happened so we can attempt to replicate it. If it's complex, please include screenshots where possible:
Accepted a reverse breeding request from user #49900, who provided the required food bundle, toy bundle and nesting material. Rolled over my account on the third day when the cubs were born to a message saying I'd forgotten to nest my lioness and she'd lost her cubs.