How much does he weigh?
He could be hitting a temporary wall growth wise and it can be normal for a fast then.
May have nothing to do with the rats.
If if he took three he will probably happily take more when ready. I would not, personally, offer mice.
How often do you feed? You probably said, but I might have missed.
If you feed every week. Offer every 2-4 for a while until he eats again and assuming he’s a good weight.