I'm also running Windows 10 on a Thinkpad laptop, with current updates. I am not having that issue, so it's probably not being caused directly by either of those factors.
The solution is to use another browser or change your account settings to use the basic reply editor instead of the wysiwyg editor. This seems to happen every so often with browser updates.
__________________ .
You have brains in your head. You have feet in your shoes. You can steer yourself any direction you choose | Dr. Seuss
I get it all the time on this forum, using Win 7 and Firefox. I usually just edit my post afterward to delete the extra lines. Not sure I want to bother with another browser. Bad enough that I need a new O.S.!
__________________ Losing weight puts one at much greater risk of becoming thin.