I had some very similar problems, including the ones you listed having now after attempting to fix.

What worked for me was flashing 2.06 with wICPFLASHADSB. Importantly wICPFLASH did not work for me.

I never saw the message "CMD_RPD_HIGH_LOW data not match" however, so our cases might not be exactly the same.

It is quite peculiar that we had the same problem at the same time, I hope you manage to fix it too.

So initially my boards RGB software control on polychrome was fine for a bit when I used it after a few days then problems came up. The RGB color were stuck and unchangeable despite them being addressable. I currently have a tforce delta rgb SSD 5v hooked up to it. I then tried to fix it by turning all the RGB off and it did. But the problem was turning it on. Everytime I try to turn it off or do anything at all, all my motherboard rgb flickers with a white color on and off rapidly and no change happens. This happened throughout trying to do anything at all related to trying to get my rgb to work using the polychrome software. 

Now weird parts im not familiar with. These following errors popped up when trying to change any colors in the rgb software:

* list index out of bounds (238) 

* exception access violation at address 005b58d3

* exiting the program would give me : abnormal termination detected

I then proceeded to look for solutions online. Here's what I've done

* CMOS reset - does nothing

* Unistall and reinstall polychrome software - does nothing

* Flahed the RGb software using the wlCPFLashADSB bit 1.10 and 2.06 ver

I then proceeded to do another solution by flashing the rgb software and at first, it didn't work at all! Nothing happened then tried again and this came up:

wICPFLASH v1.0.20 - ASRock Incorporation, all rights reserved

Project Name = X470 taichi

BIOS Version = 1.50

Reading file: nu51_1.10...0...ok.

Enter ICP mode.

Company ID: 0x000000DA, Device ID: 0x00210050

Erasing:     EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE

Programming: PPPPPPPPPPPPPPPPPPPPPP

Verifying:   VVVVVVVVVVVVVVVVVVVVVV

CMD_RPD_HIGH_LOW data not match

"**FAIL**"

    

So that didn't work and then I tried the other flash in the bin

wICPFLASH v1.0.20 - ASRock Incorporation, all rights reserved

Project Name = X470 taichi

BIOS Version = 1.50

Reading file: nu51_2.06...0...ok.

Enter ICP mode.

Company ID: 0x000000DA, Device ID: 0x00210050

Erasing:     EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE

Programming: PPPPPPPPPPPPPPPPPPPPPP

Verifying:   VVVVVVVVVVVVVVVVVVVVVV

Exit ICP mode.

Program done.

and it worked! Lights turned on but there's a problem. They were addressable but they were out of order

* Changing IO cover rgb section = it would change the audio rgb section instead

* Changing PCH heatsink rgb section = it would change the IO cover section 

* Changing audio rgb section = it would change the half side of the addressable rgb on the delta SSD 

* Changing addressable rgb on the delta SSD rgb section = it would change the other HALF of the SSDs addressable rgb

* The PCH heatsink RGB = unaddressable at all. No parts of it can be modified.

Also noting when trying to flash the nu51_1.10 file, it has no affectation as if it was useless even when run again it doesn't say fail anymore. 

Help please? :(

TL;DR - RGB software worked properly abit then didn't. Transitioned to possibly hardware problem. Flashed rgb software and worked again but addressing each RGB part addressed a different part in the mobo instead.