User error, checked the wrong file
Thanks for reporting! Engineer team is looking into this issue.
I just tested it and the download (as well as the same version 3.211-1227 I already had) matches the sha256 checksum displayed there.
Maybe something is tampering with your downloads? (or gl-inet has fixed the issue already?)
No, I am stupid. I went with the Creta instead of Slate. And Additionally I realized I must first upgrade one minor version and then the autoupdate will work.
Apology for cying wolf!