Please ensure that you are using latest AMD driver(For Windows 10).Refer Issues with Photoshop Lightroom CC/Lightroom 6 and certain AMD drivers | Windows
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Also Could you please create a new catalog,import few Pictures and then check if Lightroom still slows down after several minutes of usage.
Guesses: turn off face detection; turn off sync with Lightroom mobile.
Also, there was a thread on this exact topic, maybe 3-6 months ago, modifying keywords slows down and takes forever. I don't remember if a solution was found, but I suggest you search for it.
This is the the topic dj_paige is referring to:
You can also try working with the Metadata panel completely closed. Right click on any Develop panel header and uncheck 'Metadata.'
Thanks for the quick response. Sorry, I forgot to mention that I did indeed do a complete uninstall/reboot/reinstall of the AMD driver (current as of today). If nothing else seems to work I'll try the new catalog tip.
@dj_paige: Thanks for taking the time to reply but yes, face detection and sync with LR mobile are off. I'll search for that other thread.
@trshaner: You have saved my life (well at least my sanity)!!! This tip did the trick! I turned off the metadata panel and now keyword editing and picture selection works quickly with no lag or wait time. It had been set to display all IPTC/EXIF values and I can see now how that must slow the system down. I will need to be more judicious in my use of the metadata display.
Thanks to you all!
Glad to hear that resolved the issue!