Sources marked as falseticker which shouldn't be

Hi,

I've met a strange situation. I have 3 stratum-1 ntp servers driven by
holdover atomic clock, just mark them as A, B, C.

After several months, ntp server A has 2~3ms offset with the other two, and
the clients(both ntpd and chrony) marked A as falseticker, which is
expected behavior. Root dispersion of each ntp server is about 1.4~1.7ms.

But some of the chrony clients also mark B as falseticker, some marked B as
combined, some marked B as selectable but not combined, and all chrony
clients select C as current time source.

Offset between B and C are small enough(currently 200us~300us). According
to selection algorithm, I think B shouldn't be falseticker?  'chronyc
selectdata -a -v' shows like this:

[image: chronyc_selectdata.png]

On ntpd clients, the selection algorithm works as expected: A marked as
falseticker, B and C are randomly selected and the other one marked as
combined.