bug#39967: 27.0.90; how to debug point moving erratically?

[Eli Zaretskii]

> From: William Rankin <william@bydasein.com>
> Date: Sat, 07 Mar 2020 13:49:33 +1000
> 
> I've been on the emacs-27 branch for about six months, and every now and then
> the point will begin erratically jumping around the current buffer without
> input. (I only got to addessing it now due to the impending release of 27.1.)
> 
> Some observations: This only happens about once a week. C-g has no effect.
> There's no clues in *Messages* buffer. Point movement is beyond visible 
> portion
> of buffer. It usually happens in emacs-lisp-mode buffers that have been open a
> few hours, but I've experienced it in other modes too.
> 
> It seems like it could be font-lock/jit-lock moving point around outside of a
> save-excursion, but I know no way of confiming this.
> 
> How should I go about debugging this?

Find the feature you load/activate in your init files which causes
this?