Unable to Uboot update AR750s with 3.105 but with can 3.104

Unable to Uboot update AR750s with 3.105 but with can 3.104. I am using .img files from http://download.gl-inet.com/firmware/ar750s/release/

Forgot to mention I think it might be related to this issue since the 3.105.img file is 16.91 MB, over 16 MB, while 3.104.img file is 15.73 MB

Yes this is a bug. As uboot has been shipped with the device you cannot upgrade it (you can but risky).

So you are advised to flash 3.104 the upgrade 3.105.

Uboot will be upgraded and shipped with new devices.