Having problems connecting the cores

Hey guys, I’m working with the spark core for a while and for some reason lately I find it difficult to connect the cores to new network. (I tried from CLI and from the app on my iphone). Did you have any changes lately? Do I need to update the cores?
I didn’t changed anything and I have been working with around 30 cores (and more) since last July.
I will love to hear your opinions.

What do you mean with “new network”?

Have you problems with your old one, too?
Could it be due to interference/overcrowding on the new channel?
Could it be due to any of the reasons mentioned in the Troubleshooting docs?