Yeah, I just noticed it is only happening with Chrome (or Chrome-based Edge). Not including the empty alt or title tag appears to be the most reliable way of preventing Chrome from being wonky on this.
I've deployed a quick work-around on my sites which does this;
There is XF\BbCode\Renderer\Html::$imageTemplate which is dumped into a sprintf statement as output when lightbox is disabled (ie the editor). My Lazy Load [img] add-on manipulates this, but I'm willing to bugfix it
Kicking that to using the template system instead of a hardcoded sprintf statement would be nice.
Looks like in XF 2.2 gold getAttachAlignClass was replaced in favor of using processImageDisplayModifiers values. If you have code using getAttachAlignClass then take a look src/XF/BbCode/Renderer/Html.php in renderTagAttach for what you need to update.
(I got caught in having add-on that worked fine with the betas but not the gold release. Whoops. )