Well, I have been at this for hours. The admin bar on the front-end disappeared a few days ago and today I decided to try to hunt it down. I have disabled all plugins. Deleted a suspicious Visual Composer (who I still suspect of some involvement) and uploaded the latest version, same with the main site theme. But it's gone on my subdomain sites too. I have had every plugin disabled and reverted my subdomain to 2015 theme and still it's not showing.
Also - Appearance > Customize - doesn't work - and I really need it. It does work however if I disable 'Domain Mapping" plugin, which is mission critical important.
PS - clues.
-suspected visual composer because I could not deactivate it - behaving very buggy - updated now seems better
-some plugin conflict with SEO yoast. Every time I activate it it talks about opengraph settings conflicting but doesn't say with what.