Intensity Pro 4K card suddenly stopped detecting the device

I have been using my Intensity Pro 4K capture card without any issues for several weeks now. A few days ago, it stopped detecting the device. I had changed nothing, so I assumed that it was the repeater connector that I was using to connect the 2 HDMI cables between the camera & the capture card (someone did step on it).
I ordered a new one & when it arrived I tested it again, only to find that the system still did not work. I connected the camera directly to the card with a short HDMI cable (under 1m) and it did work...but it didn't work with any cable longer than that. This is strange because previously, a longer cable (up to 8m) worked fine without the need for a repeater.
I have managed to get a longer cable working intermittently after reinstalling the software.
I also ensured that all Black Magic software was enabled at startup.
Why has it suddenly stopped working?

After speaking to the technician at BM, he suggested that I not use HDMI at all but rather use micro converters HDMI to SDI. This will cost me another $300, plus I'm not even sure if this will work either.

SPECIFICATIONS:
Camera - Sony Nex VG20 (tested on 2 separate identical cameras)
Software: Blackmagic_Desktop_Video_Windows_10.9.5 (later versions don't work at all)
Computer:
Windows 10: Version 10.0.15063 Build 15063
GRAPHICS CARD: NVIDIA GeForce GTX 970
PROCESSOR: Processor-Intel(R) Core(TM) i7-4790K CPU @ 4.00GHz, 4001 Mhz, 4 Core(s), 8 Logical Processor(s)
MOTHERBOARD: ASUS Z97M Plus
MEMORY: 32GB

Any suggestions are much appreciated.

So I ran some more tests and somehow got it to work on the extended HDMI cable!
Unfortunately after unplugging and trying with another identical camera, it stopped working & I couldn't get it to work again, even on the original camera.

So it seems that the issue is intermittent.

I found a way to make the Intensity Pro card detect the camera on an extended HDMI every time (I think).

Disconnect & reconnect the HDMI cable at the back of the computer. Turn the camera on.

Strangely it works with one camera & not the other even though the cameras are identical.