To be fair I think its just part of life having shit interviews no matter how experienced you are. I finished my degree and postgrad degree in a STEM field and currently work at CERN in Switzerland. I had a job interview today in London (which I flew in for) that went fucking terribly. Like literally supposed to be a 4 hour interview, 2 hours in the interviewer comes back in and say \`We aren't going to continue, thanks a lot' and just shows me the door. Felt like a fucking idiot and just sat there like 'oh really' Best advice is to just crack on, and now that when the right position comes along you'll do just fine