First off, sorry for the problems everyone has been facing with the error recovery system. We added the feature in 2017b where upon encountering an unknown function or identifier, MATLAB will search through a users "current working directory" history and make suggestions based on that. Unfortunately what could sometimes happen is that some items in that history could no longer be accessable, causing the delay you're seeing here.
The workaround, as you already know, is to remove those problematic directories from your history. Though we understand that it is still frustrating and not always realistic since some directories could become innaccessable as your working and still cause an initial delay. We've been seeing more and more of this feedback from customers, so we are going to take some steps to try to alleviate this problem in a future release. We're working on it!