Rodent Pro is one of the only suppliers I won’t order from due to multiple gross looking shipments of rodents I’ve received in years past. I know not all have had problems but it was enough to implore me to look elsewhere. For what it’s worth, I agree with your vet that the snake’s body condition looks fine. Certainly doesn’t look underweight by any means. Simalia are pretty lean built animals, even including boeleni which are a bit heavier built than most of the other Simalia species but still a relatively lean snake.
Also, better to weigh prior to a feed/after a bowel movement if you feel it necessary to get that accurate of a weight on your animal. Weighing 4days after feeding will give an inaccurate estimation of the animal’s true mass.
I was pretty sure Rodent Pro is one of the suppliers I've seen various complaints about- I'm glad you brought that up.
Also agree with you that the snake looks okay in the pics- but I don't discount the OP's observations either- not everything is obvious from photos.
Rudeness is the weak man's imitation of strength. Eric Hoffer(1902 - 1983)
“The greatness of a nation and its moral progress can be judged by the way its animals are treated.” ~ Gandhi