Where you ever able to get a solution to this, we are also experiencingthe smae issue.
Tried to create support ticket in the cloud portal. Web form gives "Server Error" when I hit submit. 
Our Desktops Error - Unable to load policy. I have successfully deployed by master agent and manually at other customers.
I have been working on a test PC at the customer network. Installation fails on all WIndows 10 PCs with Unable to Load Policy. Checked the forums here and tried suggestions others had so far.
I have done the following:
1. Made sure on the latest windows 10 Pro build and updates.
2. Removed old AVG with clean up utility.
3. Examined host files and group policies on desktops.
4. Bypassed all security engines on the firewall. (Sonicwall - my other clients have sonicwall too)
5. Whitelisted all addresses and ports on the firewall as listed in preparation documents.
6. Disabled windows desktop firewall.
7. Enabled file and print sharing on desktops.
8. We have no proxy settings configured.
9. Tried installation on multiple desktops.
10. Desktops at office - unable to load policy.
11. Tried installing on a desktop at remote site location with it's own internet connection. Same thing.
The servers at this customer deployed with no issue and I was able to setup master agents, etc. Any attempt to manually install or deploy through master agent never installs on any desktop.
Snip of log from this machine: (I get 404 and 500 errors in the logs on any Windows 10 Pro machine)
02/06/21 17:08:18 Administ Setup - Setup > ClientVersion = 4.23.138, DeviceID = 613150
02/06/21 17:08:18 Administ Setup - Setup > ParentProcessId = 3604
02/06/21 17:08:18 Administ Setup - Setup > ParentProcessName = avg_business_agent_setup_offline.exe
02/06/21 17:08:18 Administ Setup - Setup > IsSilentAction = 0
02/06/21 17:08:19 Administ Setup - Setup > CDownloadInstaller::GetDownloadUrl()=
02/06/21 17:08:19 Administ Setup - Setup > CDownloadInstaller::BuildDownloadedInstallerExeFilePath()=C:\Users\administrator\AppData\Local\Temp\7zS41E31D98\avast_business_antivirus_setup.exe
02/06/21 17:08:19 Administ Setup - Setup > ParentProcessId = 3604
02/06/21 17:08:19 Administ Setup - Setup > ParentProcessName = avg_business_agent_setup_offline.exe
02/06/21 17:08:19 Administ Setup - Setup > IsSilentAction = 0
02/06/21 17:08:19 Administ Setup - Auth > PROXY COPIED (host=, port=0, use=0)
02/06/21 17:08:20 Administ Setup - Auth > Existing installation has invalid database (C:\Program Files (x86)\AVG\Business Agent\smbpol.db)
02/06/21 17:08:20 Administ Setup - Auth > PostDevice(device_status_id=1)…
02/06/21 17:08:20 Administ Setup - Auth > <- Reply to devices, HTTP Status = 500, Reply {"timestamp":"2021-02-06T22:08:20.254471Z","errorCode":null,"traceId":"601f1354041fddca318c5b09ce8df0f6","details":"Unexpected server error"}
02/06/21 17:08:20 Administ Setup - Auth > PostDevice failed (Resource = devices, HTTP Status = 500, Headers Content-Type: application/json; charset=utf-8
Hi Lamb,
We are sorry to hear this.
We will help you to resolve the issue.
Are you referring to the AVG Free version or the Business edition?
Please provide us the screenshot of the error message to investigate further.
You can post the screenshot here in your topic. Click on "Answer" & then click on the "Image" [mountain symbol] & follow the instructions.
Keep us posted.
Where you ever able to get a solution to this, we are also experiencingthe smae issue.
Hi Lamb,
We are sorry to hear this.
We will help you to resolve the issue.
Are you referring to the AVG Free version or the Business edition?
Please provide us the screenshot of the error message to investigate further.
You can post the screenshot here in your topic. Click on "Answer" & then click on the "Image" [mountain symbol] & follow the instructions.
Keep us posted.
Hi Edd,
We are sorry to know this.
We will check and help you to resolve this issue.
Are you using AVG Free version or AVG Business Edition?
We request you to create a separate AVG community post by clicking the link below and post your questions in your own post, so that we will check with your AVG account and help you with additional support.
https://support.avg.com/support_ask
Thank you for your understanding.