I have something similar to this with deadlifts and I found it to be mainly because I have damaged my left hand previously and my grip is rubbish. After a few reps my grip starts to diminish so I start to compensate by jerking the weight more. After a set or 2 I get a real burning sensation there and a struggle to stretch my arm out without it hurting. Wrist straps have definitely helped and I try not to do as many reps now and focus more on a slower and more control rep.

You’re talking about the muscle between the bicep and tricep that adds separation between the two right? A good way to activate it is very slow hammer curls. I’d assume pain from deadlifting would mean you’re accidentally slightly bending your arms too much or you’re trying to almost row the weight with more tension in the arms than the back. I’ve had it before but below the elbow because my elbows were flaring once I got past the knees.

That is weird for deadlifts. I've smoked my pecs, traps, all kinds of shit in my up shoulders from deadlifts. Like molin said everybody is different, maybe your biceps were still tight from a previous workout. I alt grip 99% of time myself.