I can’t speak about the Intensity Shuttle, as I’ve never used one. I use other BMD products instead without difficulty. So, what’s different about the Intensity? The computer? The software? USB3 issues? I have no idea. I’ve used a BMD component-to-sdi mini converter into a BMD mini recorder without any difficulty (no USB at all). I used BMD’s own capture software on trailing edge (for 2015) hardware. Neither the MB nor CPU for that machine are available for sale now. That’s how trailing edge it was. It’s the machine I’m writing this on. 
I’ve since upgraded to recording video on a BMD Hyperdeck Shuttle, which is also now discontinued. Again, no difficulties at all. All my experience with BMD products has been the same: rock solid performance.
So I can’t explain your difficulty at all. You could try asking for help on the BMD support forum. Maybe there’s some issue with the computer you’re using. If so, they can do more to help you with that than I can.
So my advice earlier, and the advice below, is based on the assumption that you’re using BMD products like the kind I’ve used. If nothing I offered before helps you…all I can do now recommend is a standalone BMD solution. I expect that that would be very expensive but effective and totally reliable. I.e. don’t use a computer for either playback or recording video. Only reliable standalone devices.
As for the LZX side, I hope you’re not playing the image or video from the same computer that records the VC output. If you are, I think that could be the source of your problem. This is why I recommended a TBC earlier.
Regardless, I’ve found the VC input to be very sensitive. This is another reason for using a TBC. There certainly used to be TBC devices that cost much less than €800, but they’re much harder to find now. You can find some on ebay “preowned”, but even the models I used to see sold new only a few years ago are now discontinued.
So your best option might actually be an LZX module, when such a module - either the original TBC or the forthcoming TBC2 - becomes available.