supplemental update

I attempted to update from 10.15.5 to the 10.15.5 Supplemental Update, but after the second reboot, I got this error: macOS could not be installed on your computer An error occurred installing macOS. To use apple Diagnostics to check your Mac hardware, shut down, press the power button, and...

Here are my hardwares: 7700K+asus z270 prime-a+gtx1070 (connected to a 21:9 monitor via dp port).Everything works fine on 10.13.2(17C88). When try to update to 10.13.2(17C205) via APP store, (I've even tried using the standalone dmg file), system goes into updating mode automatically, saying...

I installed High Sierra with Unibeast 8.0 It all went fine. Then I downloaded the supplemental update and it goes through the installation and once rebooted it shows still the macOS Build 17A405. Anyone have had this same issue?

So i just updated ML 10.8.2 with the latest supplemental update. Lo and behold, what once took less than 10 seconds to boot (I use a samsung SSD) now takes more than a minute!! Please, anyone, tell me what could be going on here and how do I go about fixing it. Please !!!