Did you manage to solve this?
I'm having the same problem now.
Still no. Looks like there are some changes with hosting parameters. I've checked it local and it worked. But it still don't work at my main hosting.
Looks like a big JS problem...
Try turning off the compress_js and maybe compress_css System Settings.
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discuss.answer
Finally fixed it with my web hosting. It was a problem with php_flag directives in my .htaccess files (my web hosting has cPanel administration panel and it conflicts with php_flag). After commenting of php_flags my TinyMCE started to work again.