macOS Sierra FileVault enabled freezing at login
My MacBook Pro (Retina, 13-inch, Early 2015) has been consistently freezing at login with FileVault enabled on Yosemite, El Capitan and now Sierra (all clean-installed). When the login screen appears I can eventually type a password and log in but everything is extremely slow and unresponsive. I tried turning FileVault on and off but it would help only temporarily. Now that this issue returned on Sierra again I'm starting to get worried. Any ideas / pointers for a fix?
MacBook Pro, macOS Sierra, FileVault