@steve_togo 

Not seen this myself, but reading your post the first thing came to my mind was MU-MIMO with OFDMA.   If OFDMA is loading the subcarriers and fragmenting the delivery of your printer packets over said subcarriers, this may appear similiar to airtime fairness.    Given the printer transfer rates will be much slower than other devices, its got more chance of being split and subcarriered in this scenario.

Hopefully that makes some sense, as said not based on any trials just thinking out loud..  not sure how or if you could test this tbh..

  @Philbert Thank You! you were correct. This raises 2 questions, I read the white paper about OFDMA and according to that the AP chipsets should be very fast to split the carriers.

1. Does TP-Link have a firmware bug? They are not able to process things quickly.

2. Why are they not able to determine that the link is not capable of OFDMA and switch back to legacy transport when communicating with that client.

Apart from the above 2, there is another bug, Disabling OFDMA does not work. We need to reboot the AP for it to take effect.

With all the above being said what is the use of Wifi 6 if legacy devices wont work  and we have to disable the Wifi 6 features. I regret upgrading my AP now.

  @steve_togo 

Hey

1. Does TP-Link have a firmware bug? They are not able to process things quickly.

I would say that is the least likely reason for this, from experience Printers have awful WiFi cards and likely its the client side that is causing this issue.   OFDMA is not a "new" technology, its been around for years but only recently built into WiFi.   Its actually part of the chipset feature set and is usually on by default so unlikely to be anything TP Link has done here, the chipset will either work or not in respect. this is also likely why it needs rebooted to change this..  gut feeling this is the Printer side compatibility issue.  

Again thinking out loud, OFDMA is designed to load as much onto the airspace per subchannel as possible for maximum efficiency, something like a printer which requires a slow consistent feed of data would fall as low priority and have say a theoretical 5% of the substream for its data.  When OFDMA is enabled, the printer would need to unpack a lot of packets to find the small fraction that it actually requires, it may simply be that it overwhelms the hardware capability of the printer WiFi Card.  I know OFDMA doesnt work well on really old G/N grade hardware, this printer is likely using that for WiFi, they reported massive packet drops due to the lack of de-capsulation capacity at the client side.

2. Why are they not able to determine that the link is not capable of OFDMA and switch back to legacy transport when communicating with that client.

This is done at the chipset and is how the datagrams are arranged during stream, switching it on and off randomly would completely mess with guard intervals / timings on the WiFi.  Without going into the deep dive (its too late tonight for that :) ), its simply not possible to do, its either ON or OFF

Bear in mind that disabling OFDMA will have an effect on performance, it can sometimes be as high as 40%

You could also try checking to see if the printer has a setting to not process printing until the entire job is cached locally.  I know HP printers years ago needed that enabled when PCL6 came out for a similiar reason, it also didnt like recieving jobs piecemeal.. caching on the printer then start printing fixed that.

  @steve_togo 

Your printer is connected to 2.4Ghz? Or 5Ghz?

I think it also could be a compatible issue with Wi-Fi 6?