Click on Recent Documents. Documents all shown but on many I get the window coming up informing me it - Does not Exist?
Does not Exist
Recent Documents thumbnail shows, where a certain file was stored to, when you saved it the last time (hover over the thumbnail and you’ll see the location of the file, which is LibreOffice aware of). If a procedure (or you) moved the file to some other directory of your file system (or a document has been deleted), then the link underlying the thumbnail points to nowhere and you get “Does not Exist”, which in fact means, “Does not exist, where LibreOffice knows, it has beeb at the time of last save operation”.
In other words: You need to use your file manager to search for the file.
If you recent documents are all held in a network location then you probably need to mount the drive first.
In Windows you can do this by clicking on the drive in Explorer first, after that the drive is available