Hi @Luke1404,

The HDMI over IP devices (I assume you have either HDBitT or HDBaseT) can generate a lot of traffic on a switch and it's best to avoid this.  HDBitT is probably the worst for a switch because it has a broadcast feature that allows one transmitter it to be used with multiple receivers.  From what I recall the HDBitT guidance is to use it on a dedicated switch or at least a switch where the extender's data can be 100% isolated.  HDBaseT is point to point with it's own POC so it's not really intended to work with a switch.  HDBaseT can push 18Gbps for some video formats, so you can see how that would be a problem on your hardware.

I don't know that the data packets and the HDMI packets can coexist nicely and if they do, one or both may not work optimally given you have a shared physical wire linking your two switches.  If you want to try to make it work, you'll need to isolate the traffic, prevent the HDMI data from consuming all of the bandwidth and hope that things usually work.

Better to run another cat6 cable (or more) or try a wireless extender.

  @D-C 

thanks for the reply. The switch in the loft is essentially isolated. the cable runs from the router tonthe switch and then from the switch is the NVR and extender. neither of these have issues. 

the downstairs switch that is connected to a different port on the router and not connected at all to tye loft switch is the one that has connected devices with issues. 

whilst i know this isnt true isolation there is no need for anything from the main switch downstairs to go via the router to access the other switch