802.11s Mesh on TP-link RE450?

I've bought a couple of routers with good OpenWRT support: the Linksys EA8300, TP-link Archer C7 and TP-Link RE450. I was trying to install the latter as a wireless bridge. However, whenevr I choose 802.11s mode for the 5 GHz radio, I get the status 'wireless is not associated'. Every other mode works: access point, WDS access point, WDS client, et cetera.

I've installed complete WPAD, Wolfssl mesh wpad, et cetera, to no avail.

Does this mean my RE450 simply isn't meant for 802.11s networking?