Some other people reported issues years ago: https://www.reddit.com/r/ipv6/comments/1bzfqzn/2600_is_no_longer_pingable/ Cogent. 'nuff said.
some times actual engineering tells more than politicl theory $ traceroute6 2600:: traceroute6 to 2600:: (2600::) from 2001:418:1::62, 64 hops max, 28 byte packets 1 r2.sea.rg.net 76.805 ms 0.387 ms 0.319 ms 2 r1.sea.rg.net 0.335 ms 0.297 ms 0.253 ms 3 2001:550:2:13::16d:2e 1.406 ms 1.337 ms 1.271 ms 4 be2579.ccr22.sea02.atlas.cogentco.com 1.153 ms 1.046 ms 1.007 ms 5 be5823.ccr31.slc01.atlas.cogentco.com 21.332 ms 6 be6640.ccr82.slc03.atlas.cogentco.com 21.874 ms 23.092 ms * 7 be9563.ccr82.den01.atlas.cogentco.com 31.272 ms 31.689 ms be2353.ccr81.den01.atlas.cogentco.com 32.385 ms 8 * * * 9 * * * 10 port-channel2717.ccr91.cle04.atlas.cogentco.com 55.437 ms 55.553 ms 55.502 ms 11 port-channel9258.ccr91.dca04.atlas.cogentco.com 67.533 ms port-channel9259.ccr92.dca04.atlas.cogentco.com 67.553 ms 67.528 ms 12 * * * 13 be2713.agr61.iad02.atlas.cogentco.com 69.661 ms * 14 te0-0-0-12.nr61.b014476-2.iad02.atlas.cogentco.com 69.179 ms 69.284 ms 69.097 ms 15 2600.cogentco.com 70.695 ms !P 70.168 ms !P 71.392 ms !P similarly via ntt then on to cogent randy