Boarding from what gate?

At the airport for a business trip, I settled down to wait for the boarding
announcement at Gate 35. Then I heard the voice on the public address system
saying, “We apologize for the inconvenience, but Delta Flight 570 will board
from Gate 41.”

So my family picked up our luggage and carried it over to Gate 41. Not ten
minutes later the public address voice told us that Flight 570 would in fact be
boarding from Gate 35.

So, again, we gathered our carry-on luggage and returned to the original gate.
Just as we were settling down, the public address voice spoke again: “Thank you
for participating in Delta’s physical fitness program.

Boarding from what gate?