I installed Libre on my Chromebook by installing Linux and them Libre Office. I noticed that a simple copy/paste of a cell, row, column results in a new line being an object, not a cell. As a result, I cant do anything with it, neither edit its contents, nor even delete is as a cell delete.
Looking for help.
You probably have a clipboard manager that can handle only a limited number of formats; remove it or disable it for LibreOffice.
Some other utilities such as youtube downloaders also intercept the clipboard so check for those too.