CMK version: 2.0.0p16 (cre)
Server OS version: Ubuntu 20.04.3 LTS
Client OS version: Windows 10 Pro 21H2
Error message: Either Empty output from agent at 192.168.1.111:6556 or Service Check Timed Out
Output of “cmk --debug -vvn hostname”:
Checkmk version 2.0.0p16
Try license usage history update.
Trying to acquire lock on /omd/sites/pp16/var/check_mk/license_usage/next_run
Got lock on /omd/sites/pp16/var/check_mk/license_usage/next_run
Trying to acquire lock on /omd/sites/pp16/var/check_mk/license_usage/history.json
Got lock on /omd/sites/pp16/var/check_mk/license_usage/history.json
Next run time has not been reached yet. Abort.
Releasing lock on /omd/sites/pp16/var/check_mk/license_usage/history.json
Released lock on /omd/sites/pp16/var/check_mk/license_usage/history.json
Releasing lock on /omd/sites/pp16/var/check_mk/license_usage/next_run
Released lock on /omd/sites/pp16/var/check_mk/license_usage/next_run
Loading autochecks from /omd/sites/pp16/var/check_mk/autochecks/tin1-hp.mk
+ FETCHING DATA
Source: SourceType.HOST/FetcherType.TCP
[cpu_tracking] Start [7fd2a9116d00]
Connecting via TCP to 192.168.1.111:6556 (5.0s timeout)
[TCPFetcher] Fetch with cache settings: DefaultAgentFileCache(base_path=PosixPath('/omd/sites/pp16/tmp/check_mk/cache/tin1-hp'), max_age=MaxAge(checking=0, discovery=120, inventory=120), disabled=False, use_outdated=False, simulation=False)
Not using cache (Too old. Age is 75044 sec, allowed is 0 sec)
[TCPFetcher] Execute data source
Reading data from agent
Closing TCP connection to 192.168.1.111:6556
[cpu_tracking] Stop [7fd2a9116d00 - Snapshot(process=posix.times_result(user=0.0, system=0.0, children_user=0.0, children_system=0.0, elapsed=0.0))]
Empty output from agent at 192.168.1.111:6556
During working hours I monitor Windows 10 clients, all have check_mk_agent.msi installed with default settings and mk_inventory.vbs as additional plugin.
Firewall on each client is set to accept traffic from Checkmk server.
All agents seem to respond fine, except 1, my Windows 10 client. 
Less important, since I can locally monitor my own client, but I don’t like it that it is mostly not working.
Started 2 weeks ago according to the history of Check_MK service. On specific date it wasn’t working during the day and at the end of the day I installed the Windows update 21H2, so theoritically this shouldn’t be the cause.
Sometimes when I restart the Check MK Service on the client it works for a little while, then it stops again.
In command line I did check_mk_agent.exe test which is slow due to logs, but it is working.
Since I currently disabled monitoring of the Windows log services of all Windows clients on the server, I disabled it in my check_mk.user.yml by adding disabled_sections: [logwatch]. After which check_mk_agent.exe test was a lot faster.
On forum at latest post about similar issue the solution was to upgrade from Checkmk 1.6 to 2. But since I started monitoring from Checkmk version 2, this won’t help either.
At the moment clueless what to try next to get the Windows client agent on my machine work stable again.
Any suggestions?