Bad connections can happen with ANY connector type, especially if you plug and unplug the connector a lot.
Molex one downside is that it can be a bit of a pain sometimes to get the pins aligned properly when you push the connector into the socket - if you do that with care you should never have an issue.
One thing I HAVE noticed is that a lot of riser makers seem to "cheap out" on the soldering job, I've seen a few MOLEX risers where the MOLEX connector wasn't soldered AT ALL, just a press fit - which is a DEFINITE recipie for failure on a frequent basis.
Version 6 should be the MINIMUM riser generation to consider - not that they're more efficient, but they're more RELIABLE than anything older.
this is correct..I have molex risers version 3 from 2013, mining for 4 years already.
If you run into problems with any of your risers, I've found that in probably 99% of the cases I've had problems it was their cheap USB cable, not the riser or the PCI connector. Although I've phased out my riser use, towards the end I just bought 1.5ft USB cables for all my risers and swapped them regardless if I had problems or not. Saved me a bunch of hassle in the long run...
not just the usb connectors sometimes there are white stuff under the riser board...that white stuff is something that is left after soldering, this can conduct electricity and cause problems, people should check and scrub them off before using just to make sure.