Ok, so I've just tried the latest 0.6.45 image, and I'm getting what sounds similar to your problem... but I didn't have it with the 0.6.44 arm64 image (i.e. bionic-containers-rockpro64-0.6.44-239-arm64.img.xz)
Failing 0.6.45 boot => https://pastebin.com/fimpKEaf
Working 0.6.44 boot => https://pastebin.com/wMiyMEx5
Failing 0.6.45 boot => https://pastebin.com/fimpKEaf
Working 0.6.44 boot => https://pastebin.com/wMiyMEx5