Three gateways simultaneously not connected

I have three RPi gateways that use the basic packet forwarder.

They all connect to thethings.meshed.com.au and have been running for weeks

They all (all three of them!) stopped forwarding data on 09 August at approx 11am (UTC) - I don’t know the exact time as this is all based on the “last seen XX hours ago”.

The status page shows everything working fine.

Any ideas? Two of the gateways are behind the same public IP address, but the third is off a different IP and different ISP, so unsure where to go from here.