On Wed, 14 Mar 2018 15:44:33 -0700 (PDT),
wrote:

I stop sanding at 150, and yeah, maple's a bitch. I use a spray/wipe/spray process where I flood the piece, wait 60 seconds, then wipe all the excess away and let dry. The second spray is a light coat for colour.

Gel stains help some, too.

Hate to say it, but I would strip the rail completely, sand 80 - 120 - 150 then re-stain. While I don't usually use a conditioner, that particular piece of wood might call for it..