Latest version of Lightroom seems very, very slow...

Hi - working on W10, 32GB RAM, i7-8700@3.7Ghz, GTX1080Ti, latest versions of all software, catalogue and previews all stored on SSDs, plenty of free disk space, 1:1 previews created, files imported from Z6 as DNG... 

And still Lightroom chugs along. There seems to be a noticeable difference since the latest update on this first import.

It takes between 2-5s to switch between images in Develop (instant in Library), about 2s to activate the crop tool, quite often see "Not Responding" while waiting, which I've never seen before. The images are headshots so no massive editing going on. 

Interestingly, if I go to an older folder in the Library, performance is OK. So it looks like something to do with importing into the newest version. 

Anyone else seeing this? Any ideas?