Please describe the problem in more detail.
Please state the version number of your Lightroom installation. Do not use words like "up-to-date" or "current".
Please state the name and version number of your operating system.
im having a similar problem. im also on a custom built pc. and only lightroom and photoshop are having issues. everything was working fine for months, then a few days ago both programs started acting up. LR takes 10x longer to import than it did. Not all photos will show previews. It'll freeze at times in develop.
I hand mask layers in PS. then i try to do this (either sending from LR or in PS alone) it will start to lag. Then if I try to exit, it will take about 30 secs for the "do you want to save" to pop up, then another minute or so to actual close.
Ive run avast virus scans, malwarebytes, rogue killer, and adwcleaner and they all come back with nothing wrong.
Ive run a ram check, checked hard drive for errors, sfc scannow, updated windows, updated my gpu driver. and nothing makes a difference. This is driving me nuts.
I've talked to 3 different adobe techs who took over my comp remotely and while they did something to make it take longer for the lag to set in, it still lags eventually and freezes.