i'm at the same spot here, though i've an M8 and i'm not even rooted. i unlocked the bootloader, and installed twrp, but now i cannot access recovery mode as this annoying red message comes up while phone attempts to open recovery mode(from fastboot window) then phone just restarts. so it appears the red message is the culprit. anyway, all solutions to this message seem to assume you're already rooted, which i'm not. so i don't know how i got into this assbackwards situation, but it sure sucks lol. any ideas? as you can see, being in the wrong forum, kinda, this is tricky. haven't found any ideas, let alone under my phone. help is appreciated...
edit: eureka! i didn't download the latest version of twrp, AS THEY LIST THE VERSIONS UPSIDE DOWN!!! whatever, my fault, KINDA! okay, got that cool blue twrp screen. back on my way to rooting this thing finally! hopefully