Your case have a multiple points, I will try to comments

1. never keep in the hotel when sent a delay information, is better be in the airport, because something they improve in the delay and you will lost the flight because arrive to late to airport.
2. they can relocate some passengers in the other flight, but normally the space are limited. One Flight have above 100 passengers and the other flight at the same time but remember the other flight don’t have 100 seats free. Only a few passengers can be relocate. Unfortunately your ticket was the last in the list for Standby in the other flight. Something similar happens to me few time ago in PUJ, they relocated me in better flight but I hold economy standard ticket + Presidential I got the first in the list in the Standby.
3. The best place to see the gate change is in the airport monitor, never looks in the APP. Also remember, you need be in the gate 1 hour before of departure, if you was in the gate maybe you was able to see the screen don’t show your flight in the gate. Also when the flight is delayed, don’t apply that the plane will wait in the gate until the departure time. They are try of move rush to reduce the delay time (reduce the people affected)
4. You need submit the claim online, but I don’t sure if you will get something from Copa. Because they tells you that ready give to you a meals voucher in Cancun and you lost the flight because arrive too late to the gate.

will be great if you can publish the response from Copa,