I had a similar problem with 3.2.1. In my case, the SimpleTogglePanel has client switch type, opened="false". Any form elements in it will not be decoded in server.
I traced to SimpleTogglePanel decode logic. The logic checks the "openness" first. If "openness" is false, it only decodes itself. Otherwise, it decodes its children. Apparently the "client" switch type can not update the openness state of the server Component Object.
This should be a bug. In my case, it worked in 3.2.0.