Just one elbow?
Could be many things. A pinched nerve (semi blocked nerve passage) comes to mind. Over extension/stretch of the joint/muscle or even the hand placement or grip on the DB. Actually changing a grip can have much to do with relieving discomfort in most any exercise..
Some men have used a heating element (lotion, cream, heating wrap, etc) on a selected problem area. Keeping the ligaments, tendons and muscles warm and with a better blood supply. Bottom line, keep any body part warm for any potential problem.
Taking 2 to 3 full weeks away from DB triceps extensions might be a suggestion. Testing the elbows every few days may be self defeating. And actually compound the problem.
Good Luck.
(I've personally seen 215lb plus standing French triceps curls...BB/EZ bar,full range movement. Also seen 360 plus Skull Crushers....skull crushers are a partial rep movement. Have heard, but not seen, higher weight used in both exercises. Just to note, those two type triceps exercise are not meant for everyone. If suspecting future joint problems than may want to select different style triceps movements. Dips, with elbows close to the sides and keeping the body as upright as you can (don't lean forward)..can be one of the better triceps movements..add weight after a while)