Grammarly is thinking this:
Complaining... isn’t reason to sound any alarms.
And it is correct in its thinking.
However, assuming the passenger wasn’t complaining about the chardonnay, that’s not what you meant.
You meant:
Complaining about the quality of the flight isn’t reason to sound any alarms. And the two requisite glasses of chardonnay before
takeoff isn’t reason to sound any alarms.
Try a rewrite to make parallel. Perhaps:
Complaining... and drinking... aren’t reasons to sound any alarms. —>
Complaining about the quality of the flight and drinking the two requisite glasses of chardonnay before takeoff aren’t reasons to sound
any alarms.