Unfortunately, A1 ISP are reporting issues with Telia Carrier(Now known as Arelion). Telia/Arelion provide backbone and are classified as Tier 1 ISP contracting Tier 2 ISP's such as A1, Vivacom, etc. etc. A1 said they have opened a query and are expecting a fix, however, they are expecting it would take several days to fix (I do hope their estimate is incorrect and it takes less). It's likely Vivacom ISP have rerouted their traffic trough a different node/carrier company.

I do hope SE Network team is also in contact with the carrier company and exploring options for quicker resolution of the issue or rerouting of the traffic.