A lot of whiteboard interviews require cramming. You never use any of the 'skills' these whiteboard interviews ask for in your day job at all. As somebody with decades of experience, your best bet is to get a "cracking the interview" book and run through all the practice test questions. After all, it is basically a little exam like back in school (because apparently that is who these people want to hire.... fresh grads who took their algo class a few quarters ago....)
As somebody with decades of experience myself, I have never experienced anything like you describe. The "skills" involved in whiteboard interviews I've participated in generally consist of "writing code", "thinking through a problem", and "communicating about your process". A more intense interview might also involve skills like "understanding computational complexity" and "making reasonable order-of-magnitude estimates". It is difficult for me to imagine how someone could work as a software developer without using these skills regularly.
Then again, I never took any "algo class" or any other CS classes, so what do I know. I just think people fret way too much about getting all the details right in coding interviews, because in my experience (both interviewing and being interviewed) that just isn't the point.
