@delprong:
Thanks for your interesting report and for posting the steps how you managed to get the modded BIOS successfully flashed into your ASUS UEFI BIOS. With the exception of the added "GAN" suffix it is rather similar to the guide, which can be found >here< within the chapter "B. Methods for ASUS mainboards without USB Flashback support". As soon as I have the required time, I will add there your procedure as an alternative method without the need of the " /GAN" suffix and the usage of an older AFUWINx64.exe file.

Further investigations are required to find out the possible reason for your reported issue with the inserted NvmExpressDxe_4.ffs while running the CrystalDiskMark tool.
As first step I would like to do a deeper look into your 2 modded BIOSes, which gave you different results (the one with the NvmExpressDxe and the other with the NvmExpressDxe_4 module).
Please attach them both as *.ZIP archive or post links to them.
Thanks in advance!

@delprong:
Thanks for your PM with the download links to the requested BIOS files.
I have opened them - one after the other - and couldn't find anything extraordinary.

As you certainly know, there are a lot of possible reasons for an unstable running OS, especially when a CPU and SSD stressing benchmark software is running.
According to my knowledge is is very unlikely, that your reported issue has been caused by the latest NVMe BIOS module, which we are offering here since April 2018.
Reasons for my assessment:

1. The NVMe UEFI module is only active while booting and has no impact on the processes, which are running thereafter. Once the OS has overtaken the management of the system, it is just the NVMe storage driver, which manages the NVMe Controller and is responsable for its performance and stability.
2. You are the first Forum member, who reported here about a stability issue after having inserted the NvmExpressDxe_4.ffs module into the BIOS. If you consider, that this thread has meanwhile more than 1,5 millions of views and the big amount of NVMe SSD users, who inserted within the past 1,5 years the exactly same module named NvmExpressDxe_4.ffs, you have to admit, that your suspect, that this module caused your stability problem, is really very unlikely.

@Loud:
Welcome to the Win-RAID Forum!
I have moved your request into this better matching Sub-Forum and thread, because booting off an NVMe SSD depends on the BIOS and not on the driver.
If the mainboard BIOS of your ACER PC should be the one, which is offered >here<, it is an AMI Aptio IV UEFI one. This means, that you have good chances to get your system being able to boot off an NVMe SSD, if you follow my guide (= start post of this thead).
Good luck!
Dieter (alias Fernando)

@niro @mrandy @CompBear
Since the method how to get full NVMe support is absolutely the same for all systems with an AMI UEFI BIOS, I have merged your posts with the title "GA-Z77X-UD5H F16j 2017/11/14 with NVMe support?" into it.
The answer to the title question was: "Yes!"

@sajmonp
This is the thread about how to get full NMe support, but not about the topic "How to get a modded BIOS properly flashed".
Please post your questions about the BIOS flashing procedure into >this< thread.
Thanks!

@Spock_Shocker:
Welcome to the Win-RAID Forum!
Why dont't you try to modify your MB BIOS yourself by following my guide? It is easier than you may think
If you are unsure regarding your result, please attach the modded BIOS (as *.ZIP file) or gve us a link and we will tell you, whether it is ok to be flashed or not.
Regards
Dieter (alias Fernando)