Recently updated from LR6 to Classic. In LR6 and now in Classic when my iPhone 7 is connected to my Mac and selected as the source for Importing files, the images takes a very long time to appear in the import window (3-5 minutes or so, or never) and sometimes the Import window fails to show all images (or they just appear as hundreds of “JPG”s with no images showing, or "Preview unavailable...", or causes LR to just Quit). This is prior to actually importing any images. Import is set to New Photos. Since installing Classic, I gave in to allowing all my photos (photo library) to sync with the iCloud Drive (not LR CC) and it appears as if images I have imported previously into Lightroom 6 now look like New Photos to Lightroom Classic - and it slows things to a crawl each time I try to import any photos.
Photo library quantity: about 1050
Lightroom Classic CC 2018, 7.3.1 Release Camera Raw 10.3
Mac: High Sierra 10.13.4 (late 2009); 12 GB memory, Intel Core 2 Duo, 3.0g GHz
(My apologies if this is not in the right place or format as this is my first use of a forum.) Lightroom Classic CC — The desktop-focused app
Sorry about the delayed response and the problems you're facing with Lightroom Classic CC related to slow performance.
Have you upgraded your Lightroom 6 catalog in Lightroom Classic CC? I'd recommend that you check out this article to optimize Lightroom performance and let us know if the issue persists: Optimize Lightroom performance