I would start with soaking it... Has the frog had a sore lately anywhere around the area? Is it an impaction issue? I would seperate it from the others and I would have it tested. 90% humidity is a bit high and these treefrogs do better with air circulation. It may bee too late for that frog and to be honest I would have culled it off as it clearly is suffering. But test it or I advise you to get a necropsy done to be sure your other two are not in danger.
Michael