bug#37496: 27.0.50; C-s failing to search

[Eli Zaretskii]

> Date: Thu, 3 Oct 2019 20:32:12 +0200
> From: Jean Louis <bugs@gnu.support>
> Cc: 37496@debbugs.gnu.org
> 
> I could do edebug-defun on isearch-forward or C-s and then I got this
> below:
> 
> Debugger entered: nil
>   edebug--display-1(nil 0 before)
>   edebug--display(nil 0 before)
>   edebug-debugger(0 before nil)
>   edebug-before(0)

What commands did you type that yielded this backtrace?

> And I have observed that the isearch-forward stopped functioning after
> doing not so many editing with C-x C-q, just few. Suddenly I got the
> problem again.

"C-x C-q" in what mode?  Which command does it run?