An interesting set of problems popping up on the GL.iNet boards (which is closely based on OpenWrt 18.06.1) where certain hotels seem to have a wireless system that laptops and phones can connect to, but aren't "seen" by the repeater software.
A recent post (linked below) suggests that these hotels (IHG mentioned) are actively hiding and revealing the SSIDs of APs on a relatively rapid basis.
I don't know if the impact of this is at the driver, hostap, or GL.iNet application software. However, if/when OpenWrt users come across it, here's a bit of information that might be helpful