@RedDelPaPa Just wanted to add to this. I have 2x EAP245v3. I experience the same problem on both of my AP's after flashing firmware 5.0.4 Build 20211021.
I have since reverted to previous version on both AP's (5.0.3 Build 20210604), and since then the 2.4 GHz band have been working perfectly.

Only after separating the SSID into NetworkName_2G and NetworkName_5G did I realise it was only the 2.4GHz acting up.

@Fae Hey, thanks for answering.

The problem was first experienced on a Lenovo IdeaPad 330S-14IKB. I happened to have the same exact laptop, and had no problem reproducing the issue with both laptops. 

I sat there for about 1 hour successfully reproducing the slow network speed over the 2.4GHz before attempting a firmware downgrade(To v5.0.3). The distance to the AP had no impact on speed. After downgrading the speeds were looking normal

Afterwards I reproduced the problem on my second AP (Also upgraded to v5.0.4), on both laptops, and both worked fine after downgrading to v5.0.3.

The problem on the laptop itself were extremely low speeds, and connections timing out. For example a simple speedtest through www.speedtest.net would not finish before timing out. Streaming services as Netflix and Plex simply wouldn't play videos. (Same with every webpage really) I used InSSIDer to check the signal strength to the AP's, and both AP's showed good numbers (Between -40dmb to -70dbm depending on range)

Both laptops had updated BIOS, and drivers for WiFi. 

If you need me to I can upgrade to v5.0.4 and test on other devices aswell. (iPhone, Playstation 4, Android, MAC etc)

Can confirm, encountered this issue last night w/ 3 new Reolink cameras.  Pair of RLC-410Ws and an RLC-510WA

3 EAP245v3 APs, all on firmware 5.0.4, all managed by OC200 Controller.

Cameras work fine when wired to any vlan.  When connected to camera vlan via WiFi, would not work.  SSID for that vlan was 2.4GHz.  Will not respond to any request other than ping if on 2.4Ghz WiFi.  After much headscratching and torubleshooting, stumbled across this thread, created a new vlan and SSID w/ 5GHz only, that did the trick.  Went back to the original camera SSID, enabled dual band, also enabled band steering to nudge the cameras toward 5GHz on that SSID, problem solved.

FWIW, took the cameras to a test bench, tried 2.4 Ghz connections on APs from two other vendors, no problems.  Have not downgraded my EAP245s to test when the issue first appeared.

@RedDelPaPa same issue here. Updated from 5.0.3 to 5.0.4, Reolink E1 Pro and Lumus wireless camera connections became unstable in general and completely unavailable through the NVR. With 5.0.4, I was also unable to add E1 Pro cameras to Google Home (Lumus didn't have this issue), when I tried to enable it in Reolink's app, I received an error message: "Operation failure".

I tested all these cameras by connecting them to a different brand's AP wirelesly, no issue occured. Connection was stable, NVR could connect to all of them and I was able to add all the E1 Pros to Google Home.

I downgraded the firmware from 5.0.4 back to 5.0.3 and it solved the issue immediately, everything works perfectly since.

So for me that means something is not OK with the 5.0.4 firmware, or implements something that Reolink devices cannot handle.

Very lucky case, I'm glad that TP-Link let us go back to older firmwares.

@Fae 

No idea why I was excluded from the troubleshooting, but so be it.

It would be nice if the corrected firmware is not only sufficiently tested but also secured against all current bugs such as FragAttrack etc..

And if there are still reasonable release notes, we could consider the whole thing as a business product again.

Otherwise, I can only recommend OpenWRT 21.02.1 on the otherwise good hardware.

With kind regards 

@Fae Yes, happily.