USB live boot works fine, but only sometimes?! *mid 2011 macbook pro, dd scripted USB

hello!

so I've got a really irritating bug im hoping somebody can help me fix...
Following reading some posts here I have run the terminal dd command line and installed my iso on a memory stick.

my result at the boot menu is "mac SSD", and "backup", then on the usb side: "Windows" which is the kali boot, and also "EFI boot" this is fine every time. the usb is always recognised as two bootable sources.

I get the usual "probing edd" boot hang in all modes but "edd=off" sorts that out and kali boots up and runs fine. internet, wireless etc. etc. its all good.

the problem: It takes me at least 5-10 attempts to boot it, every time! doesn't matter how i do it. start, restart, efi boot first, straight to "windows" whatever. 90% of the time i get a white screen and then nothing. then i keep trying again and again and it will suddenly boot and run flawlessly :confused:


im sure I've just overlooked something silly... hoping somebody here can help
thanks guys!