(short answer) Save yourself some trouble and just back off brake two or 3 clicks. See if that solves problem. If not dig deeper.
(long answer) I had same problem, about 10 degrees difference. I wasn't sure if bearing or brake problem but I was keeping a good eye on them. Same tires, same air pressure, same miles on same brand of tire etc.
One day when driving along there was an rest area coming up and nobody behind me for a long ways. Sort of up hill to the off ramp to rest area. I stopped without using any trailer brakes. Just exhaust brake till it cut out about 25 mph then coasted and at very end has to use little ER brake on TV only. Then I took temps. Obviously it has been long time since trailer brakes heated up anything. Temps should all be same was my reasoning.
The one that was running hot was the same as the other three. That told me it was a braking issue. Couple days later was at good spot to back off two clicks on star brake adjustment thing and now runs same temp as others.
I did ask the same question on here and got answers basically got two type of answers.
1) Don't worry about 10 degrees.
2)And don't worry about it because if it is the brake, it will wear down in 2 or 3 thousand miles and will solve the problem itself.
