I know this is an old thread, but we just solved our longtime Zebra printer connecting problems.
We're running iAP-OS 6.4.2.6-4.1.1.8.
Our printers would work or not work somewhat unpredictably.
I started checking firmware versions and found that on version 20 firmware they worked on iAP 104/105 networks and failed on iAP205/275, while older version (18 or 19) work fine on either.
I opened a ticket with TAC to see what was different from 105 to 205 that might cause this, and they gave me this reply:
We have seen similar issue with Zebra printer running running V20 firmware version. Could you check this and if possible try downgrading the firmware.
The "fix" of downgrading the printers works, but it impractical for us to do quickly, so we went with the "fix" from the iAP of turning on "legacy-mode" in the RF settings at those stores which have V20 and iAP 205
The long answer from TAC (for the technical minded):
The issue that we found in v20 was related to AMSDU frame aggregation. We saw that the v20 client did not respond to ADDBA (add block ack)request frames from Ap during BA negotiation. The fact that they worked on 105 is because AP 105 does not allow A-MSDU frame during aggregation. Other had 205 does allow this .Per standards the AP can inform this by setting the field in the ADDBA frame. This works fine on all clients but seems to be problems with v20 ones.
You should try disabling MPDU aggregation on the AP which will most likely make them work with 205.