I have seen posts related to this one, but not exactly the same (previous post always referred to copy-paste problems in writer, this post is about Calc). I am using libreoffice 18.104.22.168.0 on Fedora Core 31 linux.
When copy-pasting within the same document, the following problem occurs:
The first copy-paste works fine, but then at the next copy paste, the value that appears when pasting is the one from the previous copy, and it is pasted as an image.
Then the third copy-paste works again as expected but the fourth one pastes the value of the third copy and again as an image.
My workaround right now is to click copy twice, this seems to solve it, putting the right value on the clipboard.
After erAck’s answer, I checked, and as far as I know, I do not have any clipboard manager installed apart from what comes by default with Fedora.