When I kept BPs, I noticed that unlike many other kinds of snakes I've kept that will happily eat multiple items with no questions asked, many BPs will refuse to eat more than one item per meal.
And on forums like this, many others have reported similar behavior- which is part of the reason why many try to convert their BPs to eating rats- so that just one rat of the appropriate size will be taken per meal, rather than having the second item refused as wasted, & having the meal be inadequate.
I strongly suspect that up to now, you've just been lucky. Young BPs are normally better feeders than adults- time to meet your maturing BP.![]()