Lightroom Classic: Very slow rendering in Develop module

hi folks,just installed LR CC. Rendering in develop module is really slow. Eg. when I move between photos, it takes a good 3 seconds for the photo to fully render. Displays "loading" for about 2 seconds and then a further second or two before the image is fully rendered.This isn't happening in the Loupe view.This is with a new set of photos I just imported, and I had "build 1:1 previews" set during import.Is this an issue or have I got a setting wrong somewhere?It wasn't quite this bad on LR 5.ThanksDave