Device offline - HIK CONNECT

Hello,
Strange problem I'm facing.

Got a 60 camera setup on a large site. Been working fine for months

Today, they called and said the app is showing device offline.

I have checked and it is indeed showing DEVICE OFFLINE on all cameras.
However, If I click PLAYBACK, it shows recordings ... right up to the 3 minutes before the current time.
Live view on the NVR is fine,
Checked platform access and that says ONLINE ...

So I'm really confused

Everything is how it should be , it's just...

Device offline - HIK CONNECT