Boot failure after High Sierra Update

UPDATE: I'm starting to wonder if this is a hardware issue, rather than a software one, on this 2015 retina MacBook Pro anyway. A couple days ago, I discovered that the machine seemed to boot normally if I used Verbose mode (holding down command-V on startup), while it would freeze when the progress bar was about halfway across if I tried to boot normally. After several tries, however, that stopped working...

Then, this morning, after continuing to disable .kext files last night, and trying repeated reboots without luck, I found that the progress bar would go about a third of the way across, and then the machine would spontaneously reboot. It seemed like it would have repeated that cycle forever if I didn't force a shut down. Note: I was not doing a Safe Boot; I don't know if High Sierra, with its transition to APFS, does a disk check on every startup now, or what, but that sure seems like a red flag. Anyway, after leaving it off for about 15 minutes, I started it up in Verbose mode again, and it fired back up fine.

[I should note that I keep referring to how far the progress bar gets, if only in the hope that it may give a clue to someone more knowledgeable than I. I seem to remember that someone figured out, a few years ago, that the time it takes to march across the screen wasn't/isn't really related to anything about the boot process, but instead is based on how much time it took to boot the last time it booted. I have no clue as the veracity of that claim though, obviously.]

Color me stumped at this point. I'll probably call Apple later today or tomorrow and see if they think it warrants sending in for repair.

Hi

I tried all the methods suggested. The first time this happened with my Mac pro (mid 2012) I reinstalled OS and I was told my Mac isn't compatible and it got downgraded to sierra automatically. The second time nothing worked. Took it to icare (India), they deleted all my data and reinstalled El Capitan. So basically my Mac isn't compatible with high sierra. Be prepared to lose all your data if you have no backup. There is no other solution as far as I can tell apart from downgrading OS....

I´d really like to follow what you find out about the Macbook Pro 15 Retina Mid 2015.
Experiencing the same issue with boot failing, but after about 50 tries of restarts it starts up with an error message about some kernels being deactivated and a log to be sent to apple(i forgot to save this one). If its helpful i can try reboot and provide this log for you.

I´m clueless when it comes to troubleshooting a mac, but il post my hardware details if it might be helpful

Hardware Overview:

Model Name: MacBook Pro

Model Identifier: MacBookPro11,5

Processor Name: Intel Core i7

Processor Speed: 2,8 GHz

Number of Processors: 1

Total Number of Cores: 4

L2 Cache (per Core): 256 KB

L3 Cache: 6 MB

Memory: 16 GB

Boot ROM Version: MBP114.0177.B00

SMC Version (system): 2.30f2

Do you have a SDXC memory card inserted somewhere during to upgrade process?

pci pause: SDXC

Waiting for DSMOS...

You're welcome. I forgot you said you had a Time Machine backup. That's better than nothing! Hope it goes smoothly for you!

What happens if this is the case?

Both my iMacs 27” (2011 and 2012) failed to boot after High Sierra update. I’m livid! Both hard drives failed for whatever reason. My iPhone 6 has gone bonkers too after the last few updates.

Agreed :-) 200% !

Thanks All,

After all the troubleshooting i ended up doing the restore. Everything is back and running at 100%

I'm having the same problem.
Any news?
Any chances to have it fixed without restoring from TimeMachine?