Every 26 hours, Windows Defender causes system freezing

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Hi Guys,

Just figure out this might be the right place to post.


I had this mystery for several months now. a production server appears to be freezing every 26 hours. during the freezing, I can not RD to it, IIS sites hosted on it are not responding. the freeze lasts around several minutes then everything back to normal. The server is not on heavy load, has plenty available memory and disk space, up to date.
 
Yes, it's every 26 hours. Say it happened at 1AM on day 1, then 3AM on day 2, and 5AM on day 3 then keeps going till 11PM, then 1AM  again.
 
It's Windows Server 2019 Standard 1809, OS build 17763.914
 
After trying quite long time, I was able to locate the cause to be related to Windows Defender scheduled tasks.
 
In Task Scheduler, Task Scheduler Library, Microsoft, Windows, Windows Defender, there are 4 tasks listed.
 
1. Windows Defender Scheduled Scan
2. Windows Defender Cache Maintenance
3. Windows Defender Cleanup
4. Windows Defender Verification
 
#1 has one trigger defined to run at 2:30am everyday, this one works well, always run at scheduled time (at around 2:30~2:50am everyday)
#2,#3 and #4 are the tasks that run every 26 hours(none of them has trigger).  Task history shows they were running 5:02am on day 1, then 7:02am on day 2, 9:02am on day 3. Yesterday they run at 8:10pm. These time match system freezing time.
 
This results in trouble especially when they are on their 'day shift'.
 
Could anyone share thoughts on how to change the every-26-hour behavior, so that at least I can schedule them (task 2,3, and 4) to run during night time?
 
Or even better, to make them not cause system freezing, but seems that would be even more complicated.
 
Appreciate your help!

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