My theory about CPU load was wrong earlier what I thought. More weird stuff to come. I don't know has it always acting like this because I just killed Avant if something happend, but now I made some more tests. Usual Avant toolbars, but other program is seen. I can even change tabs, refresh them, do some search from search bar, everything works... somewhere.., but what I see is only background program. I can change background programs, but if I choose Avant again, then last viewed program will be seen. BUT, if I minimize Avant and all other programs so theoretically I should see desktop I see something else. I see missing part of browser, without toolbars and everything. And these webpages work. I can browse, open links in new tab and everything without toolbars. And I can bring back toolbars clicink in system tray on Avant icon (which restores minimized Avant). Then I can work as Avant should work. But if I change to another program and then back to Avant I'll get again only toolbars. So if this toolbar error comes up, I minimise everything which leaves me Avant browser content visible and clicking Avant icon in tray brings up also toolbars.
Here are also some screenshots: