In a text document my equations are vanishing when I edit them and turning into object boxes.

I have been working for some days on a technical document which includes figures and equations. All went OK until yesterday. At that point editing an equation turned it into an empty object box. Copying existing equations or opening new ones just made new object boxes. This transition process from readable equations to empty boxes is one-way. This essentially renders the program useless for writing technical documents. In discussions there are mentions of doing a safe restart. If this refers to LibreOffice, my help menus do not show anything like that. There is also nothing on the toolbar.

The operating system is Scientific Linux, which is a Red Hat variant.