On a whim I was going to send you my computer and browser details.

Checked for chrome version and noticed it was updating to the latest version.

Restarted browser, and button now appears next to "Send" as is supposed to.

Thanks for the quick support responses.

No amount of reloading chrome adds a button. 

Here's what I've tried.

1. Restarting chrome with current pinned tabs

2. Restart chrome with only gmail as pinned tab

3. Restart chrome after all extensions have been disabled except mxHero toolbox.

4. Restart chrome after remove all extensions, reinstall mxhero, then restart.

Probably more combinations too that I don't remember. I'm probably just a wacky edge case. I'll keep experimenting to see if I can figure it out.

One thing I haven't tried is disabling all chrome labs.

I'm guessing a chrome uninstall/install would fix it = last resort.