Lightroom Classic CC 7.2-7.3: Only first import works

I often split imports from a single memory card into multiple batches in order to use the rename feature.

Ever since Lightroom CCC 7.2 (and in the current version 7.3), only the first import works. When I run a second import after the first one finishes, Lightroom copies the photos to the filesystem, but never adds them to its Library. Manually using "Synchronize folder" (on the parent) won't work either.

Only when I restart Lightroom I can run another import.

This was not a problem on versions prior to v7.2.

I'm using Windows 7 64bit.