Steps to reproduce:

1. Install Zabbix Agent 2 in version 7.0.0 on Windows host (I installed via zip package)
2. Enable PSK encryption
3. Add line about AllowedKey to config file example:
   AllowKey=system.run[powershell.exe Get-Service 'Zabbix Agent 2',*]
4. Restart Zabbix Agent 2 service
5. Go to Zabbix Frontend to section Alerts -> Scripts -> Create script
6. Select "Scope" to "Manual Host action", "Type" to "Script", "Execute on" to "Zabbix Agent" and put to the "Commands" value from system.run first parameter (example: powershell.exe Get-Service 'Zabbix Agent 2')
7. Set bigger global timeout  (Administration -> General -> Timeouts) for script execution
8. Go to Monitoring-> hosts page and run your script on specified windows host

Result:

Timeout of execution script occured on frontend (see below screenshot):

Zabbix Agent stops without getting any info in logs on default debug level:

When I'm testing key via "-t" option in agent. Everything works:

Logs from Zabbix Agent with Debug level 3 and 4 are included in attachments. 

Expected:
On frontend should be visible output from requested command.

Zabbix Agent should be up and running.