LibreOffice Writer got very slow

LibreOffice Writer got very slow. I just updated it to 5.4.1.2, but that didn’t help. Scrolling is difficult and text entry has about a 2 or 3 sec lag. It is now almost unusable, but was working fine editing simple text files the last time I used it (a few weeks ago). I did reload my Win 7 64-bit system a month or two ago, but that didn’t bother anything else, and probably improved performance. The problem I am having is with some older files with several text boxes, but each file is only about two pages (about 25 to 35 KB) – I haven’t worked on these files for about 6 months, but there was no problem back then. There’s no problem with creating a new test file, and typing sentences into that. I’ve tried increasing the image cache memory allocation, but that does nothing. I wonder what happened? Thanks for any help you can offer. David