I would like to thank all of you for your thoughts regarding my brake problem. I also realize that it is difficult to diagnose a problem from afar. Nothing was making sense to me on this.
I was in contact with the supplier of the brake assemblies who had some suggestions of their own. All of these failed to solve my problem. So they agreed to send me a replacement brake assembly.
I installed the replacement assembly last Saturday but was unable to perform a test drive with the trailer until yesterday. The brake on the affected wheel worked just like the others. They were all at relatively the same temperature. I now feel confident to take the trailer out (as we are planning for the coming long weekend).
Although I still do not know what the underlying issue with the "bad" brake assembly, I am satisfied that it is working now.