First, this is a user-to-user "peer support" forum, so "we" can't fix anything.
Second, this is nearly always a user-caused problem. So "we" need to help you figure out what to do to fix it.
Please post your complete computer specs ... OS/CPU/RAM/GPU/vRAM, the number and type of drives used.
A very handy item would be a screen grab of your timeline panel's header/control block. Drag/drop that onto your reply box so we can see it in your post, and don't have to download a strange file to our computers.