See bug #474294.
If you have an x86_64 system you can help by
a) installing chrony-1.21 from Stable or Unstable and confirming the bug
or
b) installing chrony-1.23 from Experimental and determining if the new
upstream release has fixed it.
You could also look at the bug report and the source and help me find the
problem. I've had no response from upstream.
--
John Hasler