Acronis Cyber Protect Cloud, Acronis Cyber Backup 12.5: Backup fails with AGENT_CORE error "A socket operation was attempted to an unreachable network"

Symptoms

Backup or another activity fails with the following error:

 {"domain":"AGENT_CORE","code":"INTERNAL_ERROR","debug":{"msg":"Post https://dc-cloud.acronis.com/bc/idp/token: dial tcp x.x.x.x:443: connectex: A socket operation was attempted to an unreachable network."}}"