Twenty Sixteen Content Width Changed Too Narrow

Greetings…

Literally overnight the content on my site became too narrow – including the sidebar.

It LOOKS like it is stuck in “mobile mode”.

Same on all screen sizes and browsers.

Read all the articles but nothing seems to apply to my situation.

Installed the “Customize Twenty Sixteen” plugin but it makes the alignment worse.

I am loath to start messing with CSS when this site has been running smoothly for over 2 years.

Can’t really change anything with the theme customizer as it is fixed.

Checked site for hack with Sucuri but all good.

I am stumped.

Thanks for any help.

The page I need help with: [log in to see the link]