80% of the time, the user did NOT update EVERYTHING properly. The entire zip file from hekate and atmosphere has to be extracted, overwriting every file, and if you use a mod chip, your main payload (hekate, usually) needs to be extracted again to the root of your SD, and renamed to payload.bin (Delete old payload.bin first, of course).
Then you have 10% who need to update sysmodules and/or remove custom themes. (But those will get an error screen, not just black)
And the final 10% customized their .ini files, and don’t realize that using retarded all-in-one packs, overwrites their .ini files.
If you haven’t updated atmosphere in a long time, the first boot can take a while, while it clears out error reports from the SD. You may have to be patient. But rolling back atmosphere will absolutely NOT work, because FW 17 has new keys.