Filter doesn't work, what to do?

I’m editing a video and everytime I want to add a filter, my video become slow and the sound is choppy. I tried putting Proxy or the Preview Scaling but nothing works. A helping hand would be appreciated.

Could you provide more information please? Shotcut version, OS you are running? Which filter etc

Also, your system specs and the type and sizes of files you are using. Does your computer meet the minimum system requirements?