On your properties/search page, the Features & Amenities filter does not list amenities alphabetically. The top of the list may look correct, but the order breaks down further down.
Why this happens. The filter lists amenities in the order they were first created on your site, not by name. Each batch of amenities synced from your PMS is alphabetical within itself, but every new batch is appended after the previous one. This becomes more noticeable as new amenities arrive over time.