AdGuard Home shows client names on Proxmox but only IPs on Synology VM

Hi. I have two AdGuard Home instances running:

• One in Proxmox LXC container (works correctly, shows client names)
• One in a VM on Synology (which shows only IP addresses of clients)

Both instances have identical configurations, synchronized using AdGuardHome-Sync. Private reverse DNS servers are configured on both to point to my router. Reverse DNS seems to work when tested manually, but the Synology instance still shows clients only as IPs, without names.

Do anyone have an idea what could cause this?