A problem I’ve had since moving to Windows 8.1 (I skipped 8.0 and have yet to move to 10) is that Explorer can take a while to open the folder I click on. It turns out that the problem goes back to the days of the infamous Vista, when Microsoft decided to optimise folders according to their contents. To get round this issue, you need to select the folder, right-click to choose Properties, and click Customise. You will see a dropdown list headed Optimise this folder for:
To avoid the delay, select General items and click OK.