Service instability, unusable

Service instability in Essex, Md. I have a brand new direct line from the pole to the gateway. Brand new modem xfinity supplied. No splitters. Gateway is receiving 115 Mbps, but devices are dropping to < 1 Mbps with an apparent Signal-to-Noise (SNR) failure. Devices reporting poor down speeds of less than 1mbps despite 'Excellent' signal strength. I have time-stamped photo evidence of the throughput collapse. Can an official employee help me figure out what’s going on? Chat agent told me all looks fine from that side so give it two hours. I need to work. Ongoing two days now.