Globallink 520 Unreliable Logging on VRM - Telstra

Globallink 520 does not log every 15 minutes. It often goes offline for hours at a time, usually 1 or 2 hours, 4 or 5 times a day. Have had it replaced under warranty and the new one does exactly the same thing. Both units are HQ2313 despite being purchased in 2025.
I have seen this issue on this forum with no resolution. Is this normal?