Guys, I am interested in this issue.

@Pascal , can you describe your total topology with IP subnet details here?

@Tobacco 

You can follow this new post here https://community.tp-link.com/en/business/forum/topic/158837?page=1&t=2019%2F04%2F17%2008%3A32%3A36%20%2B0000

where I had reply this:

Front of the fact that some of our device are constantly disconnected  or unable to use the mix of 2.4GHZ/5GHZ we decide to create a dedicated SSID with only 2.4GHZ.

Then the issue of loosing internet access during roaming between AP was the next issue..

Apparently the Fast Roaming feature is not so friendly for some clients devices that use only 2.4GHZ .

We use bunch of EAP245 V3 and 225 V3 and we choosed these AP for the fast roaming and band steering solutions.

Once the dedicated SSID with only 2.4GHZ was removed, all the devices didn't met again the loosing internet issues.

During the test with the mixed SSID, when a user was front of lost internet access, the only solution was to manually restart the WiFi of they device
to force a reconnection and the internet went back.

We was then force to use a separate AP not from TP-Link to give a wifi 2.4GHZ to the devices that was in trouble to use TP-LINK 2.4/5GHZ_Fast Roaming_Band Steering.

We hope that TP-Link will find a way to give multiple SSID with separate settings in terms of Fast roaming/band steering/ airtime fairness or

find a way to let an SSID with only 2.4GHZ operate without interference from the other SSID with 2.4/5GHZ.

Cheers,

I see. You had observed this issue in detail.

For your scenario, some suggestions based on the current EAP design.

1. Upgrade to controller V3.1.10 from www.tp-link.com/en. It is coming soon. After upgraded, upgrade all AP firmware as well.

    Be noted that in v3.1.x the dual band SSID profiles are merged into one profile.

2. Enable roaming

    but don't enable "force reconnection". So the AP will not kick off the client even if the client doesn't follow AP's suggestion to roam.

3. for band steering, make it 15, 5, 1.

4. disable airtime fairness. (some client chipset has compatibility issue)

@Pascal 

Hi!

I know it's an older post, but I share my "solution":

I had a similar/same issue in a small network, and spent many hours on troubleshooting (different settings, different cables, etc). One ISP router, one T2600G-18 and two EAP245 v3s. I had only problems with wifi, most of the time intermittent dns errors, sometimes connection issues. Speedtests were ok, if the page loaded. I was frustrated and about to give up, when I realised something: I had a small desktop switch (TL-SG105E) that is manageable (I forgot about it), and the default management ip was 192.168.0.1 (default ip of most of the TP-Link products). In my case the problem was that the ISP's router had limited config options so I it had the same default ip -> so classic and so stupid error: a device with the same ip as the router. If there is one person who just did a facepalm, this reply was worth.

Bests

@Pascal I'm having the exact same problem as you describe.

EAP V1.2 (Fry's Electronics screwed me over with old stock) 

Connected, go to sleep wake up and phone cannot communicate to WIFI until I disconnect and reconnect. Shows full signal during that time and does not show any issues with connection. Furthermore, constantly having issues with my laptop showing full signal and good connection internet test speeds 300+ MBps but will lose connection and stop responding to web requests or access any network traffic until I disconnect it and reconnect it. 

Not sure what the issue could be.