Ntpd synchronizes but chronyd fails

I am setting up a time server with chronyd but it fails to sync.

# chronyc sources
210 Number of sources = 5
MS Name/IP address         Stratum Poll Reach LastRx Last sample
===============================================================================
^? smtp.visionnet.us             0   10     0   10y     +0ns[   +0ns] +/-    0ns
^? nist1-lnk.binary.net          0   10     0   10y     +0ns[   +0ns] +/-    0ns
^? c-73-98-218-154.hsd1.ut.c     0   10     0   10y     +0ns[   +0ns] +/-    0ns
^? clock.xmission.com            0   10     0   10y     +0ns[   +0ns] +/-    0ns
^? time-c.timefreq.bldrdoc.g     0   10     0   10y     +0ns[   +0ns] +/-    0ns

Hours later, it still can't sync.

However, if I configure ntpd on the same host with the same ntp servers it syncs immediately:

# ntpq -p
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
-lithium.constan 18.26.4.105      2 u   50   64    7   74.746   13.677   1.487
*nist1-lnk.binar .ACTS.           1 u   49   64    7   48.827    6.845   4.008
+c-73-98-218-154 .GPS.            1 u   47   64    7   12.792    2.418   1.338
+clock.xmission. .XMIS.           1 u   49   64    7   22.799   12.845   1.272
-time-c.timefreq .NIST.           1 u   49   64    7   59.498   -2.968   1.434

If I watch tcpdump during both attempts I can see that when chrony attempts, it sends a NTPv4 Client packet and I never see a response, but when ntpd does it, I see the NTPv4 Client packet and the NTPv4 Server packet immediately after.

Is there something I'm missing? Does chrony talk on any other port than udp 123? (We do have a datacenter firewall that needed a hole opened to get out, but I can't shake the feeling that there might be something else needed by chronyd)

ENVIRONMENT:

System is RHEL 7.3 patched current one week ago

Here's my chrony.conf

server us.pool.ntp.org iburst
server time.nist.gov iburst
server time.nc7j.com iburst
server time.xmission.com iburst
server time-c.timefreq.bldrdoc.gov iburst
stratumweight 0
driftfile /var/lib/chrony/drift
rtcsync
makestep 10 3
bindcmdaddress 127.0.0.1
bindcmdaddress ::1
keyfile /etc/chrony.keys
commandkey 1
generatecommandkey
noclientlog
logchange 0.5
logdir /var/log/chrony
allow 0.0.0.0/0

and for comparison, my ntp.conf

driftfile /var/lib/ntp/drift
restrict default nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict ::1
server us.pool.ntp.org iburst
server time.nist.gov iburst
server time.nc7j.com iburst
server time.xmission.com iburst
server time-c.timefreq.bldrdoc.gov iburst
includefile /etc/ntp/crypto/pw
keys /etc/ntp/keys
disable monitor
logfile /var/log/ntp.log