Find the last Library Backup for MC24, and Restore it into MC25, with both Restore Options ticked.
It sounds like to the MC25 installation didn't find the MC24 installation properly, and automatically ran an import of everything it could find from everywhere, which happens with a new installation and an empty Library. The Restore, of the MC24 Library and Settings, should fix that.
Also, make sure that your Firewall and all security software is aware of and allows MC25 to do its thing. Both would have known about MC24, but they will need to allow MC25 now.