So I've been doing my research - and from what I've gathered - the boot.img is too large, or there are corrupt blocks in the boot partition. However - what I've tested thus far makes me think this is not the case.
I am able to install 5.3 just fine. I have built 5.4 and was to start testing it myself when I came upon this error. It IS a fresh pull from CM which brought in a few fixes. However - I do not use any part of their boot stuff, as you know I create my own kernels.
I have taken the 5.3 zipfile that installs, and put the 5.4 boot image in it, and it installs just fine. This is what leads me to believe that it's not the boot.img itself.
I've also seen a few posts that blamed the recovery (I'm using RZR 2.0.3). However - again, my test should rule this out. updater_binary is the same between 5.3/5.4, so it's not that.
Sooooo - I know a few of you have faced this. Did you ever get it resolved?