I can relate to this. I have pretty good resume - good schools, advanced degree, impressive sounding projects, a long list of publications. My track-record suggests I am at least a 3x engineer.
So when I get into a coding interview, I'm expected to perform as such... but I usually come off as a 0.3x engineer. Like really bad. Forget syntax bad. Forget algorithms bad. I've bombed so bad in a technical interview, the interviewer questioned if I even knew basic trigonometry. They had spent 10 hours interviewing me prior and felt good, but got me in person and suddenly thought I was an idiot.
In each of my jobs, I've had a considerable ramp-up period. I'm talking 6 months or more of feeling completely lost and unproductive. I get in my head and it makes me perform worse.
If I'm not fired in that first period, I'm lucky. Only after about a year on the job I can perform at the level my resume would suggest.