I was reading news in GNUS and suddenly emacs started echoing in the
minibuffer:

   Error in post-command-hook (global-eldoc-mode-check-buffers): (error "Variable binding depth exceeds max-specpdl-size")

After that I could not M-x or M-: or did much to investigate, only able
to copy the last part of *Messages* to a file (attached). Not sure if
this is useful.

But this bug might be interesting. It is new. A max-specpdl-size
automatically popped up while I was idly reading in GNUS.