For a while I've been dealing with Lightroom Classic CC being extremely slow, it got to a point that it was basically unusable. Something wasn't right, I tried everything I could to fix it. I reinstalled the application, reinstalled the OS, made sure all my drivers were up to date, etc. I went to google and did some research trying to find optimization tips to speed up Lightroom and still no avail, it was the same. I then went to YouTube and tried to find videos exclusively on Lightroom Classic CC being slow and I came across one video that mention presets can actually make Lightroom slow, not just in the develop module, but the whole darn app. I haven't heard about presets being an issue before and so I did some further research and found a small number of posts on forums, blogs, etc about this but there isn't a whole lot of details as to why some presets can make Lightroom extremely slow and buggy, Adobe hasn't said anything officially to my knowledge about it. One possible idea is that Lightroom apparently has to create a preview for every image for every preset. Mind you, I didn't have many presets. 15 tops but a decent portion of them had a lot of adjustments and local adjustments that I created. I decided to just delete them all and I only kept a couple presets that I call "speed presets" that just allow me to speed up my work flow since they are often settings I apply to every image, in fact I probably could make them as an import preset. Anyways, after deleting the heavy presets, Lightroom instantly was faster and I mean it was night and day. Everything was smoother and faster going from library to develop, using the local adjustments, going from one image to the next both in lib and dev modules whereas before it would take nearly 20 seconds and even crashed LR a few times. I also noted a slight decrease in memory usage after deleting the presets. So there is obviously some kind of issue with Lightroom and presets that contain a lot of adjustments. So if Lightroom is being slow to you and you happen to have presets, I would experiment and back the presets up first and then delete them and see if Lightroom is faster. Hope this helps.