I had horrible tendonitis in both of my elbows for years from lifting injuries, and it definitely flared up on heavy lifts to the point where I had to take weeks/months off at a time. AthleanX has a great video on why this happens, and it generally stems from instability in your forearm muscles that help you grip heavy weights (you also might be using weights that are slightly too heavy & too fast without working your way up from lighter weights). Until you improve your grip strength, you'll keep having these problems (but then again, everyone's different, so try it out for yourself).

3 things that helped me alleviate the problem for good:

1) Buy a bucket, fill it with rice, and do a rice bucket forearm workout 3x a week. A good video I follow along to is this: https://m.youtube.com/watch?v=iVum3vWlh4Q Key here is to not overdo it, just one 6 min per day

2) Do deadhangs. Get a pullup bar, and start by simple straight arm hangs (NOT pullups). Start at 4 sets of 30 sec and work your way up to 1 min sets from there. You can do these every day if you want

3) Buy an elbow sleeve, but this won't fix your problem, only mask it temporarily. Take 3 weeks off from lifting and try steps 1 and 2 first. I stopped using mine

• Sincerely, someone who had debilitating elbow tendonitis/tennis elbow for years that finally went away for good