App bug with preview seatmap?
 

Was looking at a Horizon flight in the app, saw lots of seats open. Went to book on the website and only a few seats were open. Went back to the app and confirmed that on its preview seatmap it shows a lot available, but when I try to change seats on my flight it only shows what the website shows.

I'm guessing they're blocking seats for some reason (weight and balance) and the app isn't properly reflecting that...?

Are you signed in so they know you're an elite MP member? It may be some of them are blocked for elite status only?

Negative. I'm seeing the same thing. I'm MVP Gold and the app (logged in) was showing rows 5-8 on Q400 available in preview. Those are not elite status seats. I just booked a ticket on same flight for wife (she's MVP) on the website. None of the seats in rows 5-8 were available. Went back to my account on the app and attempted to book same trip for myself. Even though I was logged in already as I could see an existing reservation and my account info, the app prompted me to login to access my profile info to complete the purchase. When I did that and got to select seats, rows 5-8 were not available. So it appears the seat preview on the app is not displaying accurately until you actually attempt to purchase a ticket.

Horizon usually shows rows 5-8 as blocked on Q400's until check-in time. They sometimes block Row 20 as well. The preview often shows all non-occupied seats.

As an FYI, they used to show as blocked on Expert Flyer as well but that changed a month a go or so and now just shows them as occupied.