Avia advanced edit not showing, and disapearing text in edit

Hello
1) Avia advanced edit not showing ; see more details in private content.

2) There are blank pages in edit (visua) after update and it happens often.. Since, flagging up the issue 2 days ago, text is once again vsible in edit but as text disappears regularly after updates, it would be useful to understand why so that I can deal with it. When this happens, the page is usally visible in text mode and on the frontpage but not on visua edit. This time, i was also getting this message as well which makes no sense as no special characters etc are involved.
It seems you are currently adding some HTML markup or other special characters. Once all HTML tags are closed the preview will be available again. If this message persists please check your input for special characters and try to remove them.