To me it looked like a guy who can lift the gym "trying" to run.
Agree on arm mechanics
Back looks like it's bending over in the last half too? Like you're getting sucked into the track.
It you freeze frame around half way - it looks like you're sitting, not on a bar stool, but at times on a lounge chair!! Landing way in front of your COG.
Obviously you have the strength - You need to focus on technique, re-learn how to apply Force through a straight line from head to toe. Get your flexibility back, you might be full of muscle knotts??
Have you been doing any Mediball throws? Plyros?
Do you get regular massage or use foamrolling?
Being a full second off your PB - you could easily consider everything you did in that run today Wrong It will be great to see you do it all right and rack off a nice fast time again. Good luck