Indeed, it appears the ACF Location Field add-on has a conflict…
Deactivated everything but when i activate ACF Location Field, the WYSIWYG appears with no toolbar and the following text which i didn’t ever type:
<p><br data-mce-bogus=”1″></p>
Google Map Field (which i only recently realised was added) seems to be a replacement for the older ACF Location Field anyway, so maybe this isn’t a big issue.