A Cisco Switch configured with 802.1x, MAC Authentication Bypass, and WebAuth will always try 802.1x authentication first, followed by MAB, followed by WebAuth.
If there is an endpoint that does not support 802.1x when it tries to connect to the network, it will need to wait for a reasonable amount of time before WebAuth is offered as a connection option.
Enhanced FlexAuth addresses the problem by allowing multiple authentication methods concurrently. This will allows clients to come online more quickly.
Enhanced FlexAuth, or Access Session Manager, is a key component of Cisco Identity-Based Networking Services v2.0 integrated solution.