When you Flash your roms when you go too reboot in twrp do you have "install twrp if not installed" and "install twrp apk" checked? If so uncheck them... Also just go to reboot don't do the other options just reboot without twrp doing anything...
(I can't remember the exact wording of the options)
I was having issues a long time ago... And this was what was causing my issues
I simply select do not install.. I am installing it right now. How long you think it takes to boot for the first time?