For now could get under helloweb loaded from several places via wrk e.g.

[ 2223.320576] +cU 2001067c1254000e0010000000000001 80 00000000000000000000000000000000 00 00000000000000000000000000000000 00000000 00000001 00000000 01200200       lo
[ 2223.320601]  . U 2001067c125400000000000000000000 30 00000000000000000000000000000000 00 00000000000000000000000000000000 00000400 00000001 00000000 00200200       lo

That means that

    unreachable 2001:67c:1254:e:10::1/128 cached

was cloned from

    unreachable 2001:67c:1254::/48

in time when

    2001:67c:1254:e:10::/80

was absent.

But that unreachable route in cache was removed pretty fast, when route
for 2001:67c:1254:e:10::/80 appeared again.

Still watching...