I tried myself on windows10 with usb-serial on my iap205 with firmware 6.5.4.3 and confirmed it just works fine with normal settings. see image in attachment.
I see this familair serial issues once before and that was a hardware failure of the serial chipset.
Update your AP to latest version, reboot them to factory reset. If that isnt working create a TAC ticket. T
Note that the IAP205 has lifetime warranty when purchase after 1 dec 2015 and your the first owner ;)