Given that the longer cables within the infrastructure are working correctly but the newly installed patch cables are causing connectivity issues, the most likely cause is an incorrect pinout on the patch cables. If these cables were not properly crimped according to the T568A or T568B wiring standards, they could easily cause a failure in connectivity due to incorrect alignment of the transmitting and receiving pins. This is a common issue with DIY or newly crimped cables where mistakes in the wire arrangement can render the cables non-functional. The other listed issues, such as mixed cable types, plenum rating, or cable distance exceedance, would not typically result in a total loss of connectivity as described.