I get this error pretty frequently when using “go to implementation”, “peek at declaration”, etc. As the error suggests, it seems to be a bug in initialization - the only fix I’ve found is to quit & re-open the IDE, but if it works correctly the first time then it works correctly for the remainder of the session.
I was getting this bug in Water and had not yet reported it, and I’m now getting it in Fire as well after moving to a MacBook. I took a screenshot of the error but couldn’t copy the text. I assume the message is in a log somewhere, but I’m not sure where the log file is. I can past the text here if someone can point me to its location.