Yeah, if the light on the gateway is flashing red, it probably has nothing to do with your equipment.
But dealing with tech support, it's best to simplify down to just their equipment. I literally disconnected everything and just had a laptop with an ethernet cable going into their box when the tech showed up. And even then, the techs tried to blame the USB/ethernet adapter, so I had to dig out an older laptop with integrated ethernet ๐
We might need to transition to fiber for more than 10gb either way. The SFP+ transceiver heat issue you mention is very real. In my case it fried the port on my Ruckus switch, not the transceiver though. And that was running in 2.5gbps mode with a 3 foot cable.
Seems like you have to run conduit if you want true future proofing.