My bad. I forgot to mention (or realize) I was trying to get this to work on a custom taxonomy page, so I forgot to include get_queried_object();
Resolved now, thanks to my brain fart. Thanks for jogging my mind, John Huebner!
In case anyone else needs it, here’s my fixed code.
$queried_object = get_queried_object();
$seals = get_field('seals', $queried_object);
$countSeals = count($seals);