Hardware: hAP AC2, cAP AC
I got the Wi-Fi roaming issue on my iPhone XS MAX(iOS 12.4), while other devices like iPad Pro 10.5"(iOS12.4/13b7) and Huawei P20 Pro has no problem for roaming. My phone will drop the connection during roaming and reconnect to the nearest AP after, it was so annoying and I'd tried many solutions like Mesh them up with RSTP to control the path cost or use CAPsMAN, but CAPsMAN will slow my Wi-Fi speed from 470mbps to 370mbps, no matter how I tune the setting it's still much slower than Wireless AP mode, so I was facing 2 options either bad roaming or slow speed.
Today an idea come from my mind that "MAYBE" it was STP/RSTP which stopped my phone to establish the connection for preventing loop, so I tried to disable RSTP on both devices and boom! The issue is gone, now my phone can roam between APs with 1 / 2 pings or sometimes no ping drops.
To optimize the roaming, I use PMKID to accelerate the authentication time, and I don't need RSTP since my home network is simple enough, nothing will cause loop.
Ordered 2 x Aruba Instant On AP11 to get rid of this issue but now thinking to cancel the order since the problem's gone.