Clients won't stay connected on ac

[kai_cheung]

Multiple clients connecting to Unleashed R510 on b/g/n, not ac?  The majority of the 12 clients are only connecting at b/g/n speeds and will not stay connected via 802.11ac.  Any ideas how to force the faster 802.11ac connection type?

[soo_chung_lew]

Similar problem.. the problematic client are using Intel AC 8260, it connected to AC mode initially when the Windows start, after 5 to 10 minutes its will drop to N mode. The problem only happen in Unleashed AP, Zonedirector controller AP are working fine however.