I just rebuilt from the latest Yocto Linux from the https://github.com/Avnet/meta-maaxboard/commit/a54e9d43293a33cb7d2e58ba2eed26b7bca35235 (tip of master).
The 'uEnv.txt' problem was supposed to have been fixed in previous commit "a5a1e534326712456e53fea0b698bb89a1398bcc" but the problem still happens. I had to manually populate the file in the SDCard to get the system to boot.
Please research why this is not fixed and provide any updates in a future commit to the master branch.
Principal Embedded Software Engineer
Accu-Time Systems, Inc.