Got a CRS305-1G-4S+IN before Christmas. I've tried a couple of different sets of SFP+ modules (e.g. https://www.amazon.com/gp/product/B08NW1VBX6 and https://www.amazon.com/gp/product/B08P4MJ36T). The CRS305-1G-4S+IN is connect to AT&T's BGW320-500 router, to the single 5Gbps-rated port. The ISP/...

Exact same thing happening to me. Tried everything to fix it. Glad to see I'm not alone; however, this concerns me that this fix won't be easy, or may not even be possible. Any update on getting your issue resolved?