TIL about "Show Duplicates" - thanks! Small correction: the page you've linked to now says that "Show Duplicates" has moved to File > Library > Show Duplicate Items, which I can confirm is the case in iTunes 12.

This answer doesn't really address the question, and introduces extra information that isn't relevant and thus could be confusing, e.g. HEIF/HEVC formats.

@LangLangC I get the same behaviour as Joan on opening the lid after sleeping, i.e. keyboard backlight comes on but screen doesn't. After holding down the power button to force my MacBook Pro to power off and then restarting, I get a warning about an error with the details: "GPU Panic: mux-regs 2 3 7f 0 0 0 severity 3 WS-ready 1 switch-state 0 IG FBs 1 EG FBs 0:0 power-state 4 3D idle HDA idle system-state 2 power-level 20:20 connect-change 0 : UH eHlPH E0L H(L @ H HH : GPU is not found. PCI config access fails!!!" I'm posting this in case it can help improve this solution even further.

I've been on 10.13.6 for a while, but just lost the use of my brightness adjustment keys today. Following this process in full yet again has restored them, as @MayankChandak also reported above. I can't say what event triggered them not working when they had been, but I'm posting this news in case it helps anyone else. For the record, my 2011 MBP on 10.13.6 no longer allows SingleUserRecovery but Terminal via the graphical Recovery mode still permits turning off SIP via csrutil disable.

A quick note that Security Update 2018-003 broke my 10.13.6 MacBook Pro and I had to follow the process here again.

Just reporting in that the 10.13.5 update left me unable to boot and the procedure above allowed me to recover as usual. My dock was opaque again (as it was after the 10.13.4 update), but returned to translucent after a reboot - presumably this behaviour is due to not having com.apple.kext.AMDRadeonX3000 loaded on the first boot after re-applying this fix.

For the record, as of 10.13.4 the kexts related to AMD GPUs are: com.apple.kext.AMDLegacySupport (1.6.6), com.apple.kext.AMD6000Controller (1.6.6), com.apple.kext.AMDLegacyFramebuffer (1.6.6) and com.apple.kext.AMDRadeonX3000 (1.6.6).

Just had a bit of a mess updating to 10.13.4 and got stuck in a boot loop, but careful application of the instruction steps here sorted it out again for me. Initially after fixing the boot loop my dock was no longer transparent, but it came good after re-applying nvram boot-args="-v agc=0" - not really sure if that's what did it, or just another reboot.

Both with and without the X3000 kext loaded, I have only seen GPU temperatures of 50-60 degrees depending on load. I'm basing this on the readings reported by iStat Menus under [GPU Die - Analog]. This was even with the CPU core temperatures up to 99 degrees this evening importing photos into Lightroom (X3000 kext loaded at that time). I have also not experienced any issues with sleeping and waking, regardless of how I sleep, whether closing the lid or using the menu command.

I had already upgraded to High Sierra before my most recent problem, and I have not noticed any consistent problems relate to sleeping and waking the MacBook Pro. That said, there have been a few times when I’ve opened it up and it has appeared to boot from scratch, but I put that down to the battery having completely discharged while it was left asleep. I’ll try to pay more attention to it and report here if I notice anything relevant.

Worked on a MacBook Pro early 2011 that's on its fourth GPU/motherboard replacement - thanks!

So how did it work out in the end, @Sonja? Good outcome?

This is getting messy, but have you been through the other questions linked to this one? The answer to apple.stackexchange.com/questions/221630/… that suggests following Apple's advice here looks like it might be a chance for you: support.apple.com/en-us/HT203828. I know you said your iPad is already updated to 10.0.2, so the advice about updating to 9.3 isn't relevant, but the rest might work for you.

Ah, I'd forgotten about needing the password to turn of Find my iPhone/iPad - I assume this was what prevented you from signing out of the old iCloud account? I've added a screenshot to my answer showing what I saw when I signed out on my iPad. Sorry I didn't think of that when I was advising you to log out and log back in :(