As you mentioned before, the case of the CPU throttling to allow the battery to charge faster could be very well the reason why this is happening, and at this point pretty much you tried all the troubleshoot steps that we recommend for this scenario.
On the following link you will find the graphics driver for the Intel® HD Graphics 5500 controller, not sure if you tried those drivers already, but I Just wanted to make sure you tried the right ones:
Beta driver 4539:
Also, you can try the graphics driver from HP, on the following link you can get that driver, I looked for it but it gave me an error message saying that there are many results for "HP Envy"
As an option you can try to get in contact with HP directly in order to check if this problem is actually expected and that is how the laptop works or if maybe a BIOS update will fix it or they might have an specific driver for this type of issue, because remember that all the features and functions of a laptop are created by the manufacturer so they might have different troubleshoot steps in order to resolve it, maybe there is a setting on the BIOS to prevent this situation.
Also maybe there is an specific driver from Nvidia that is required, so here is the link for their drivers:
From our side to provide the drivers above is the best we can do for this matter, so please try them and let us know the results.
Any questions, please let me know.