If it was me and I'd gone over the whole leg and foot including the shoulder, and couldn't find any swelling or warm place or sore bit, I'd rest him completely for a few days and only take him out to empty himself on a leash.
If that didn't sort it I'd seek professional help.
Best of luck with it. Those hard to trace lamenesses can be annoying.
(with the hot weather and all check for cracked pads under his feet and if you've been doing roadwork, for thin spots in the skin of his toe pads. These would show as tiny smooth circles near the front of his toe pads)