Lightroom Classic v11.5 : Fast export but very slow add to current catalog!

When I export large number of files to a folder, like 300 to 500 files, the export to jpg with watermark is very fast, the folder is fully populated after a short time. 

But if I ask to add exported the resulting files to the current catalog, the files are very very slowy added to the catalog, it takes about 1/2 hour for 300 files! If I do not ask to add files to current catalog and I manualy ask to scan the folder, it is many times faster!

The problem is easily reproducible!