Libreoffice frequently freezes

I did three things:

Under Tools > Options > View I increased memory for LibreOffice from 20 to 200 MB (have 4 GB on the machine) and memory per object from 5 to 50 MB

Under Tools > Options > View I turned off hardware acceleration and anti-aliasing. Reasoning that there may be a bug where it runs algorithms that depend on acceleration and the machine did not have it.

Under Tools > Options > Advanced I turned off the Java virtual machine. I could not find any Java VM on the machine so I thought it best.

For the last 24 hours under quite heavy use have not had a repeat of the problem.

If you have lot of images in your document, you can try compressing it. Right Click on the image, select Compress Image option. Change the parameters to suit your needs.

If that doesn't help, try splitting the file into several small files like each chapter in different file.