Why does a newly launched site either work or not?

Question

Network administration

Deployed the site via Heroku yesterday, the domain name was purchased from GoDaddy.
Initially, everything worked somehow incomprehensibly, i.e. it worked on some browsers and devices, but on others: periodically there was a message that the site would be launched soon, then there was a redirect to the site of the GoDaddy domain provider.
Yes, I have never deployed sites before, so everything is for the first time ...
Please tell me in which direction to look now in order to debug all this and the site worked continuously without these incomprehensible shutdowns.

Answer 1

The DNS may not have been updated yet, they are updated within 24 hours.
It may also be cached in the browser, try clearing it.

Answer 2

If the domain ping shows the correct ip, look towards the cache.
The cache must be reset both in the browser and in the OS.
It also does not interfere with restarting the router, but it is advisable to turn it off while the computer is restarted.