Hyper Data Protector (Hyper-V VM) "Failed to connect to 'vm'. Role: Job Manager. A network error occurred."

Hello, I have a QNAP TS873AU with QTS version 5.2.3.3006, and a PC with Windows 10/ all within the same LAN. I want to perform a backup of Hyper-V VM’s
I have configured HDP, but the first backup attempt failed with the error “failed to backup vm.” I disabled Aware Processing, and the process started, but it stayed at 10% for quite a long time with no data being transferred. After a while, I noticed the disk was overloaded, and soon after, data started being transmitted through the network interface. The Job Status menu showed the same behavior. The size of one VM was successfully transmitted, but then the following error appeared: “failed to backup vm” and “Failed to connect to ‘vm’. Role: Job Manager. A network error occurred.” This issue occurred with the second VM, but the third VM was successfully backed up.
All 3 virtual machines actually have an identical configuration.

What could be the cause of this error?