If an enormous creature polymorphs into a smaller creature and they were already carrying a medium or heavy load, would their new sizes' carry weight modifier cause them to be unable to move?
I.E.
For the sake of the question at hand, say an adult red dragon (STR 31, huge) is carrying 5000 LBs of weight (medium load), and polymorphs into a medium human. A medium creature with the listed strength can only carry a maximum of 1840 LBs - so would this dragon in humanoid form suddenly be completely unable to move?
EDIT:
After I made this post, I recall once reading something that stated that if you were carrying a light load and polymorphed, you didn't have to worry about encumbrance in your new form. If the dragon listed above were carrying 2000 LBs instead (a light load in dragon form, but still too much to even move in humanoid form), would it not have to worry about the carried weight?
Items either resize to your new size if you changed into a similar shape, or meld into your shape if your new shape is dissimilar. While turning into a human isn't typically going to cause your equipment to meld with your form, it should if your original form is a dragon. If the equipment is melding with your form, then you retain the encumbrance negatives you suffered before polymorphing, but they don't otherwise effect your carrying capacity. So you could be at heavy encumbrance and pick up your entire heavy encumbrance worth of weight without suffering additional penalties.
https://paizo.com/paizo/faq/v5748nruor1fm#v5748eaic9tl1
Short answer, your human would be impacted as if they carried a medium load, but would not otherwise apply the melded weight to your carrying capacity limit.