That's one reason not to panic or run to the vet* after just one food refusal (*unless you have time & money to burn): it takes time to play "detective"
with a snake that isn't eating. There's often a good reason that they know but we don't. Snakes help teach us patience & better observation skills.
And btw, when I first started keeping snakes I kept copious notes, not weights but everything else. (I blame it on nurse trng) One day a more experienced
keeper paid me a visit...she saw their "diaries" & had a healthy giggle over it, then asked me how I found the time? All my snakes still have a basic record
of their origin etc, but other than that, I only note things of significance (not every meal or shed). Experience tells me when to take notes. And as long as
a snake looks & acts healthy, I couldn't care less what they weigh. (same goes for me, lol...I gain about 5 pounds over winter, & swim it all off doing laps
all summer, no big deal)
So maybe he has some retained shed? or is shedding again? Good reason for him to pass on dinner. One tricky place that some snakes fail to shed is their
chin & I can imagine that would feel strange & signal to them not to eat until it's removed. Now & then, one of mine does that, & I have to help him, that's
how I know. It's a place they HATE to get help with, so it takes a soak & patience with gentle restraint, letting go frequently rather than over-powering the
snake, until the job gets done. You might try keeping him restrained in a "critter cottage" (smaller side cage) with wet moss or wet paper towels + shallow
water for a while, then see if there's retained skin you can help him with.