This problem took me awhile to solve, so I am sharing both the problem and solution here. I searched, and found, some helpful discussions on the internet that pointed be in the right direction (see solution), but nothing that actually provided explicit instructions for solving the problem.
The problem occurs in ArcGIS Arcmap 10.5.1 running on Windows 10.
Episodically throughout the day, ArcMap will make the whole system become unresponsive, whether it is running in the foreground or background. Even the mouse cursor lags, moving in spurts. If ArcMap is in the foreground, the table of contents panel turns grey, and then flashes white again 5-6 times. After this 10-30 second episode, the system returns to normal operations.
This has occurred regularly for me in ArcMap for the last 5 months since I started using this computer. It is not a huge problem, but drives me batty as it happens every couple of hours throughout the day.
Best Answer
I searched for answers for awhile until the following discussion pointed me in the right direction: https://community.esri.com/thread/208892-arcmap-1041-freezes-in-windows-10
I haven't had full freezes or crashes as others report, but the problem appears to be related to the Group Policy updates received over my work's network. I verified this by manually updating the group policy by running GPUpdate.exe (windows key + type gpupdate), which immediately triggered the problem in ArcMap.
Group policy updates default to every 90 minutes with a +/- 30 random offset to prevent all computers hitting the servers at once. I tried fixing the problem by changing the frequency of group policy updates to daily, but they still occurred every ~90 minutes. What did work was enabling 'Turn off background refresh of group policy' which prevents group policy updates while the computer is in use. The group policy updates are then applied when you logoff (locking computer also seems to work). You might want to check with your IT dept to make sure this is okay.
To change this setting, you will need to run the group policy editor with administrative privileges, which you can access by hitting windows key, typing gpedit.msc, right-clicking the gpedit.msc file that appears, and 'run as administrator'. In the window that pops up go to Computer Configuration > administrative templates > system > group policy Right-click Turn off background refresh of group policy, select edit, and toggle the 'enabled' radio button. Hit okay, and close the windows.
You can monitor your group policy updates by running the 'event viewer' with admin privileges (win + type 'event viewer'), and going to Applications and Services Logs/Microsoft/Windows/GroupPolicy
I hope this helps. If you don't have admin rights, you might see if an admin will enable this setting for you.