MP 7,1 Problem connecting 3 Radeon Pro W5700X 16GB monitors

[MacBS]

Hello everyone,
I just bought an AMD Radeon Pro W5700X 16GB graphics card on eBay for my 2019 Mac Pro 7.1.
The problem is that this card is supposed to support 6 screens,

(I have three 27-inch Iiyama monitors (ref: Prolite B2783QSU)).
So where's the problem with connecting three?

My setup with this card is as follows:
1st screen connected to the card's HDMI port, which works.
2nd screen connected to a Bus 0 port (with a USB-C adapter).
3rd screen connected to a Bus 1 port (with a USB-C adapter).
Of the three connected screens, only the one connected via HDMI works.
The other two remain black.

I tried connecting the USB-C cables to the top of the Mac Pro, as well as to the top rear panel.
I also tried the other two screens, which are only recognized via HDMI.
The refresh rate on HDMI remains the same. (Maximum 60 Hz)
For the next two, I can adjust them (maximum 69.88 Hz), which
I did, but without success.

Could someone help me or explain why?

Sincerely.

 

[Bigwaff]

Do the displays appear in System Information app under Displays or either the Thunderbolt buses?

 

[reader50]

Which USB-C adapter are you using? Not all USB-C devices are created equal.

 

[MacBS]

Which USB-C adapter are you using? Not all USB-C devices are created equal.

Here are the cables used for the MPX W5700
For the 3 screens:

1 HDMI to DVI 4K cable
1 DisplayPort cable + USB-C adapter
1 DisplayPort cable + USB-C adapter

Attached are photos of the two adapters.

Best regards.

 

[choreo]

I purchased a 2019 Mac Pro new in July 2020 with a W5700X card pre-installed. I have always had (3) 27" monitors connected since the beginning (no problems). In the beginning I had (3) NEC QHD monitors and I ordered (3) DisplayPort x USB-C cables from Monoprice to connect them (no adapters). The past couple years I switched out all three NECs for new 27" 5K ASD's (using their included USB-C x USB-C cables) - no problems still. I have never used the HDMI port, only three of the four USB-C ports on the W5700X card. My first "guess" would be the adapters - I had some problems when first setting up until I ordered the right dedicated cables.

 

[reader50]

Could you give us a link to the adapter you are using, on Amazon or wherever you got them? That's what I was asking for, so we could check the specs. And the reviews, like if other Mac users reported problems with them.

For example, your adapter might be for DisplayPort to a USB-C monitor input. The opposite of what you're using them for. Not all adapters are reversible.