Problem in my post editor

Switch to another theme. Then test your editor.

Never use theme with Visual Composer and bunch of other plugins.
I have seen that in True Mag also, this is caused by poorly coded themes and plugins.
Today, they just use bunch plugins, some code and give them money.

-But, your case, try just to upload fresh files of WordPress and see what happens, try disabling plugins, one by one.
I know, its not easy to change theme if you have manually coded some things, use custom fields etc.
If you are not, just change it than.