It could be a few things in all honesty, it could be bone spurs rubbing against the tendons and causing a tear / you may have an inflamed tendon or muscle in there causing you to have too little subacromial space, again causing a partial tear / or your form could simply be off causing too much pressure on the joint. Either way, it's best to have an MRI done to diagnose the problem sooner rather than later. You don't wanna go out from a rotator cuff injury.

I had a partial tear a while back, and went through PT to help. One of the absolute best things I did for myself was to significantly warm up the shoulders before any upper body workout and then finish off with some strengthening excercises such as dumbbell or band rotations to strengthen the muscles around the shoulder (teres major and minor). One I did this for a few weeks. My shoulder felt better and my bench press actually went up. I would also do arm rotations and stretches. Just some helpful tips for you!

I had similar pain during a rep on incline—very sharp burning pain in front of shoulder, finished the rep and did light workout. Had an mri a little while later and it was diagnosed as partially torn rotator cuff and surgery wasnt recommended. Was able to workout at pretty much same level for a few years and then it slowly got worse. About 5 years after the partial tear, i had the same burning sharp pain during incline db’s. This time it was completely torn. Basically the pain is from bone spurs compressing against the tendon and tearing it. It is the type of pain where you know immediately something is wrong.
The shoulder is complex so your injury could be totally different, but reading your description reminded me of my tears.

Do you regularly use 4 plates when training - ie. is your body use to it?

Definatly sounds like a tendon issue...try icing it that might help some..does with my elbows for sure when they act up

Often these pains are due to overtraining. Incorrect movement can be dangerous for the joints. Do a week's discharge, stretching.
Take a break with the heavy loads, even if this will be difficult (it happens to me lol)
If the pain persists, go to your doctor.

It could be tendonitis or a lot of other things. Best to get the Docs opinion to be sure!

Everyone here is spot on, tendonitis.. I've had it a few times.. nsaids to reduce inflammation, just have to stay off it for a while or go easy.. when it happened to my chest I would do light weight and always warm up on fly machine helped me alot then transition to bench.. if I went straight to bench it would hurt me alot more.. hope you get well soon bro

I have a similar problem when using flat bench. Mine is diagnosed as tendonitis. Proper warm up, turmeric supplements, and some physical therapy has kept me in the game. Hopefully urs isnt worse than that. Good luck brother keep us posted w ur results..

Either a biceps or an aggravated torn labrum, most likely. A labrum can be torn for a while without even noticing it, then one day, bam, it acts up. I wish I had more to offer, but I’ve honestly never had shoulder pain from any sort of pressing, including the flat bench. All I can really offer is potential technique fixes if that’s the issue that caused it. I’m not making any assumptions because I haven’t seen your technique, but the bench press is probably the single most commonly incorrectly performed exercise in existence. If it’s as simple as a quick form fix, that would be great news, so that’s not a bad thing.

There’s an older thread where you mentioned a strained front delt? Is there any similarity in indications?

Had the same thing. I went to the doctor and he told me my bicep tendon was torn at the shoulder. Not saying that’s what had happened to you. There a are a few things attached to the shoulder. I stayed off my shoulder for three weeks and then worked my way back with rubber bands and light weight. To this day I barely ever shoulder press with a barbell. Dumbbells don’t put as much pressure on my shoulders.