By “background” do you mean you’re doing “headless” Pano or HDR (or both if they both allow it) or something else?
Turn off the GPU in LR / Prefs / Performance and see if things respond better.
Also try changing LR’s shortcut to start LR6 with a lower priority that gives the UI more CPU:
I (and a few other users on another forum) have experienced severe slowdowns in Lightroom 6.01 (both CC and perpetual license) when the PC is connected to a network but the internet connection is down. This persisted until I rebooted my router and once it was up lightroom was snappy again instead of 30 seconds to switch photos in develop module.
well then adobe better works on this because im not always online. all this forcing me to be online is getting on my nerves anyway and is nothing but a annoying PITA.
as to the GPU.. i tried with and without GPU support... did not help a thing. :('
with backgroudn tasks i mean all the stuff that was praised to work in the background so we can keep on working.
i don´t know maybe a 12 core xeon system is needed but on my (for a consumer) pretty fast system i can not keep working while LR is doing panos or hdr.
You're still not saying what "background tasks" means, specifically.
I've been trying to replicate my issue with incredible slowness when not connected to the web. So far I can't. The web connection may need to be down in a specific way to cause the issue.
Anyway I'm back up to speed.
I just posted the same issue about "busy cursor" and "not responding" while our Internet was down. I found a dubious workaround, but this really needs to be fixed properly.