Why can zabbix agent fall off during backup?

Question

Zabbix

With a frequency every day at 2 a.m. when the backup is in progress, the Zabix server loses the agents of this machine and the virtual machines on it
With an error in the agent log

zbx_execute_threaded_metric(): TerminateThread() for vfs.fs.size[E:,...] succeeded

Monitoring of the vm machine through zabbix proxy
Restarting the agent is cured, but not always sometimes it is downloaded with the words the channel is closed, the machines are on windows server 2019
Tell me where to dig even the ideas end.
Upon completion of the backup, everything works like clockwork
Backup regular files I shove into the archive and throw into the shara over the network, while the gigabit channel between them does not strain from above 500 Mbps at the peak