I am teacher and I tried using Blynkcloud together with nodemcu at my School. Somehow the Firewall/Contenfilter blocks the Blynk cloud. I had the same problem at a diffrent school an in public Wifis. I event tried to set an exception in the Schools network filter (blynk-cloud.com) - didnt work.
The topic below is about a mobile ISP blocking some Blynk traffic…
I’d start by adding the actual IP address of your local Blynk server (obtained by pinging it) into your whitelist. If that doesn’t work then show the above topic to your IT department and see if they can assist in unblocking the relevant ports.
If that doesn’t work, then maybe set up a local Blynk server?
Pete.