I've been troubleshooting a strange wi-fi issue with a 2862ac which is in my home network. My trade is that I'm a 3rd line network technician, with over 30 years experience. I'd thought I'd seen everything until now....

The scenario is 5GHz and 2.4GHz on same SSID. 2.4 GHz works fine, 5GHz is troublesome. In particular the wifi connects, and apparently gets an IP address, but sometimes cannot communicate to the router for a much larger time period after connecting that you would expect. This particularly affects Apple devices (Late 2016 MacBook pro, iPhone 6s, iPad Air), but I've also occasionally seen it an old Windows laptop. I also note the thread here from a couple of months ago about Apple Wi-Fi issues. However the Wi-Fi is correctly negotiated at both 2862 and MacBook end - see the detail in the scenario below.

It's easier to explain with a scenario so here is one:
V2862ac [3.8.8_BT] serving the same SSID on both frequencies, plumbed to LAN1. Serves DHCP.
Late 2016 Macbook pro on Wi-Fi (negotiates 'ac', about 4ft from the 2862)
Old HP laptop on Wi-Fi (5Ghz capable but only 'g', also about 4ft form the 2862)
Windows desktop, wired direct to the 2862, port on LAN1.

Macbook continuous pings router LAN1 IP and the desktop.
Windows Laptop continuous the router LAN1 IP and the MacBook
Desktop pings the MacBook continuously.

On MacBook manually disconnect wifi (option click wi-fi icon choose disconnect), note that all pings affecting the MacBook start to fail as expected.
When the problem bites it then manifests itself as follows.....
Manually reconnect wifi from MacBook. It usually negotiates quickly, and at 5GHz.
Pings from desktop and windows laptop to MacBook start to succeed, as does the ping from MacBook to desktop - all good so far...
BUT... ping from MacBook to V2862 LAN1 IP or attempting to route through it to the internet fails, for what could be from a few seconds longer to often a couple of minutes.
Throughout the above the Windows Laptop continues to ping the V2862 over wireless, but might miss a few pings...

The fact the the Windows Laptop can ping the MacBook quickly suggest that the MacBook wifi really is up as soon as it should be.
Similarly the fact that the Windows Wired Desktop can ping the MacBook suggests that the V2862 5Ghz wifi is up.
The inability to ping the lAN1 IP from the MacBook or to route from the MacBook through it suggest that the V2862's firmware is temporally blind to the MacBook. (remember that The windows laptop is successfully pinging the router when the MacBook cannot).
During the problem, the 2862 confirms the MacBook is negotiated (in the connected station list) and the MacBook confirms it's connected at 5GHz, with an IP address)
The same tests connected as 2.4GHz connected rapidly and reliably.
When the problem is evident, the MacBook Wifi diagnostics suggest connection rate is as expected and stable as is connection quality is also stable - neither dip when the issue is evident.

(TBC)

(Apologies for adding to my already long post, but the details are important)

Things tried...
Confirmed settings are identical on 5GHz and 2.4GHz, EAPOL left enabled, Band steering off.
Flattened the router config (re-installed the .rst file for the 3.8.8_BT firmware then reconfigured by hand (ouch!)) - the issue was then seen again after minimal re-configuration. (I'll talk about 3.8.8.2_BT firmware in a mo...).
Tried various combinations of 5GHz and 2.4GHz (renamed the unwanted SSID out of the way during these tests).
Most wifi settings left at (or varied and returned to) defaults.
Channels hard-wired to deconflict with other nearby wifi.

Having gathered the above info was considering how to engage with support when the 3.8.8.2 firmware was released (supposedly just a hastily released emergency security fix). Installed 3.8.8.2_BT (retaining configuration). 5GHz seems significantly more stable but still not perfect....

SO....
Can anyone relate to the above issues? Indeed - could these be related to https://forum.draytek.co.uk/viewtopic.php?f=19&t=22011
Does 3.8.8.2_BT contain more fixes (over 3.8.8_BT) than just the security fix?

x64

As I've posted elsewhere I've found that Apple devices just don't play nicely with Draytek AP 5GHz - and the symptoms make no sense to me. e.g. at the moment I have an iPad pro connecting to an AP902 on 5GHz. The download speed, which was working fine last week, has again reduced to about 500K, I can access Google on Safari but I can't access my 2925ac on 191.168.1.1, I can't browse my music folder on my NAS but it's fine if I use 2.4GHz...the list goes on.

Agreed. I've just turned off 5GHz WiFi completely. Wake me up when they fix the problem...

maxwellhadley wrote: Agreed. I've just turned off 5GHz WiFi completely. Wake me up when they fix the problem...

I’m glad I’m not going crazy! I was just about at the ‘don’t use 5GHz’ stage myself before 3.8.8.2 unexplainably bought me enough stability to soldier on.

I’m thinking that in the early post connect period, 5GHz wifi can bridge OK to other interfaces but packets cannot route or be consumed by the V2682.

One additional snippet of information. At connect time, just when you should see the ping to the router start to succeed, One ping DOES succeed. Then you can get a few mins of failiures untill the pings kick in solidly. In that downtime bridged devices can communicate with the mac, but routed or router consumed packets cannot.

Anyone from DrayTek care to comment?

x64

A bit more experimentation - I set a 2862ac up as an AP in place of the AP902. My iPad mini connected to 5GHz and achieved full download speed (as an aside, I persuaded my ISP to reset my DLM profile and I'm back up to 37Mbs - result ). So it appears that in my setup there is a difference between the AP902 5GHz and the 2862ac 5GHz, but whether that is a physical difference or some setting which I haven't discovered I don't know.