Are you currently feeding Henry's First Cut hay? If so, the ESC is 5.9% and the Starch is 2.9%. I know how difficult it was for you to source hay and when we reviewed this hay analysis we discussed that if Po showed signs of being foot sore that you would try soaking this hay and this is what you currently doing.
This is from your post #198473
"I have no idea why. His diet is balanced, his hay is being soaked for 12 hours, and he's on PQ"
The recommendation is to soak the hay for 1 hour in cold water or 30 minutes in hot water. I wonder if the hay may be reabsorbing sugar from its "bath" water.
Here is a link to a file on hay soaking and if you search the archives you will find numerous posts on the topic.
I ask other Members to weigh in on the hay soaking time recommendations.