Unfortunately I have to disappoint you, the error does not exist
You have reported a non existing bug.
Output from my 1.6.0p17 agent with plugins and with the configuration i posted before.
(base) PS C:\Program Files (x86)\checkmk\service> .\check_mk_agent.exe test
<<<check_mk>>>
Version: 1.6.0p17
BuildDate: Aug 31 2020
AgentOS: windows
Hostname: MYHOSTNAME
Architecture: 64bit
WorkingDirectory: C:\Program Files (x86)\checkmk\service
ConfigFile: C:\Program Files (x86)\checkmk\service\check_mk.yml
LocalConfigFile: C:\ProgramData\checkmk\agent\check_mk.user.yml
AgentDirectory: C:\Program Files (x86)\checkmk\service
PluginsDirectory: C:\ProgramData\checkmk\agent\plugins
StateDirectory: C:\ProgramData\checkmk\agent\state
ConfigDirectory: C:\ProgramData\checkmk\agent\config
TempDirectory: C:\ProgramData\checkmk\agent\tmp
LogDirectory: C:\ProgramData\checkmk\agent\log
SpoolDirectory: C:\ProgramData\checkmk\agent\spool
LocalDirectory: C:\ProgramData\checkmk\agent\local
OnlyFrom:
<<<wmi_cpuload:sep(124)>>>
[system_perf]
......
Sophos_Message_Router running/auto Sophos Message Router
Sophos_Clean_Service running/auto Sophos Clean Service
<<<>>>
<<<windows_tasks:sep(58):encoding(cp437)>>>
TaskName : \Adobe Acrobat Update Task
Last Run Time : 08.09.2020 07:36:34
Next Run Time : 08.09.2020 09:00:00
Last Result : -2147023829
Scheduled Task State : Enabled
TaskName : \Adobe Acrobat Update Task
Last Run Time : 08.09.2020 07:36:34
Next Run Time : 08.09.2020 09:00:00
Last Result : -2147023829
Scheduled Task State : Enabled
........
<<<winperf_if:sep(9)>>>
Node MACAddress Name NetConnectionID NetConnectionStatus Speed GUID
MYHOSTNAME 00:15:5D:BC:47:79 Hyper-V Virtual Ethernet Adapter vEthernet (Default Switch) 2 10000000000 {63C10024-A852-4627-B24A-BD6E1E0B7294}