Curiously does this issue occur on multiple devices such as multiple smartphones, tablets, or computers? Have you tried to reboot the system and well as the router by unplugging the power cord for two full minutes, then plugging both back in?
I'm glad to hear that a reboot resolved the issue! It could be that the router or the system was experiencing a hiccup, which a reboot can help resolve. Unfortunately without digging deeper we would not be able to identify the root cause.
Having said that if the issue returns, please let us know and we can dig a bit deeper to isolate the root cause! Thanks!