My outdoor dining area has some ceiling mounted speakers made by Niles. Hurricane Irma knocked the cover off of one. It is supposed to be magnetically attached but I can't get it to stick. Anyone know of any secret to getting the covers to stay on?

So, not being familiar with that brand, I downloaded the manual. The pertinent paragraph:

The Niles MicroThin™ speaker grille installs magnetically over the speaker.
Carefully center the grill over the speaker and let the magnets do their work,
verifying that the grill sets flush against the ceiling at all edges.

Not sure how a storm would affect fit or magnets. Perhaps it bent it slightly. Note says above it's to fit flush at all edges.

Short of that, you might try some double sided tape.