Hey,
It could be caused by many things. I can recommend some troubleshooting steps which can help you. They are as follows:
1. Are you using some VPN software? If so, please stop using it and make sure you are using BB/DR on a "classic" local network.
2. Disable any antivirus software you are using on all PCs (including Windows Defender and Firewall) - this is just to check if the issue is related to this software. You can then turn it back on.
3. Add custom inbound/outbound rules in Windows Firewall - See this guide
4. Do not mix Corona's DR and Backburner. Use only one or the other.
5. Make sure on each computer there is only one instance of 3ds Max, DR server, Backburner. If there are multiple instances running at the same time (for example two 3dsmax.exe processes), some issues may appear.
6. Do not render from a perspective view—use some kind of camera, preferably a Corona Camera.
7. Open your scene, go to Render Setup, deselect the "lock" icon in the top right corner. Click on any viewport, then click on the viewport you want to render. Select the "lock" icon in Render Setup again. Such a reset of the rendered view sometimes helps.
8. Disable IPv6 -
https://medium.com/@JockDaRock/disabling-ipv6-on-network-adapter-windows-10-5fad010bca759. Go to Windows’ Services list and make sure "Function Discovery Provider Host" and "Function Discovery Resource Publication" are started. Set them to automatic start.
10. Make sure you have network discovery enabled -
https://www.isunshare.com/windows-10/turn-on-or-off-network-discovery-in-windows-10.html11. Make sure you are using exactly the same 3ds Max version on all of the computers taking part in the distributed rendering (note: even using different update/hotfix versions may cause problems, for example, 3ds Max 2020.3 vs 2020.2).
