Hi,
I'd first discard a missmatching units/scale problem:
Start a new drawing and run the insert block process, if there is nothing in the screen, then do an autozoom
Chances are that View -> Autozoom shows the block and gives a hint about what happens.
Otherwise, then there is a bug, please see if it has already been reported it in github
https://github.com/LibreCAD/LibreCAD/issuesHTH
Pere