FileVault - intermittent bluetooth connection on startup

Apple wireless keyboard and/or mouse do not work during the login process. As a temporary fix, the user must connect the keyboard to the iMac during the login stage (using the arrow keys to select the correct user, pressing Enter, and then entering the password). Once logged in, the keyboard can be disconnected, allowing bluetooth to function normally.

To resolve the mouse issue, the user must also connect and then disconnect the mouse to restore bluetooth functionality, once logged in first. This issue only arises when FileVault is enabled; if FileVault is disabled, no problems occur.