This may not be the cause of your tendonitis, but I would start here:
1) Try taking a finger wider grip. Your forearms are a bit angled in at the bottom.
2) You are bringing the bar down too fast. It's causing you to have poor control and lose tightness on the way up.
3) Focus on pushing the bar back to your shoulders sooner (some reps are going away or up too much with not enough back). #2 will help with this.
I would work on the above with lighter weight for a bit and then see where things are at.