I cannot connect my Core to internet

My Core was succesfull connected to internet last year.
Now I wanted to restart the system but don’t succeed the internet connexion anymore.
I tried via my iPhone with Tinker : no reaction although my Phone is recognizing my two chips (Core and Photon). The blue light stays blinking and I get the message no Core found.
I tried via usb : the CLI says : “done, now your system restarts”. My Core is blinking green but doesn’t go over to cyan.
I was asking for a new key with Particle Keys doctor. Succes.
But nothing changes for the internet connexion trials.

Out of interest, how do you KNOW it’s not connected to the internet?

Because the green light stays flashing without passing to Cyan.
Because I cannot have any reaction on Tinder with my iPhone.
Because there is a grey dot in front of the name of lmy Core. (that dot is coloured for my Photon)
Because I cannot flash a program via the cloud.
Etc…

Ah, sorry, hadn’t got that from your first post. My bad.

@chip, seems some cores have DNS issues. Take a look here: