Windows freeze, scroll bars disappear and reappear

Greetings, tridiaknz.

Welcome to the Apple Support Communities. It’s understandable that you’d want to be able to view your scroll bars. 

Do you have your scroll bars set to always share?

“Scroll bars appear in a window when there’s content that doesn’t fit into the window’s current size. Choose an option to control when scroll bars are shown:

• Automatically based on mouse or trackpad: Scroll bars are shown depending on the mouse or trackpad you’re using.
• If your device allows gestures, scroll bars are hidden until you start scrolling. Otherwise, they’re visible.
• When scrolling: Hide scroll bars until you start scrolling.
• Always: Scroll bars are always shown.” Change General preferences on Mac

If not, select them to always share. We hope this helps! Thanks for being a part of the community.

Sincerely.

Between what you have described above regarding disabling Bitdefender and the general improvements observed, that is proff enough that Bitdefender is interfering with the normal operations of the OS.

To add to Bitdefender interference - take a good look at the 578 posting on the ASC Forums regarding the negative effect this software has and reach ones' own conclusions

Search - Apple Community Bitdefender

Open the Activity Monitor >> View >> View All processes.

Look in CPU tab for any unusual process using a lot of CPU and do the same in Memory tab.

This may help identify any Run Away process or Application.

ASC = Apple Support Community

https://discussions.apple.com/search?q=Bitdefender