VLAN routing drop out every 4 hours on M7100

Hey all, so we have a core M7100 and 7 edge M5300 POE.  I have VLAN 200 across all switches with my voice traffic, tagged on all edge ports and untagged on all physical equipment (ShoreTel switches).

Routing occurs in the M7100 with the IP 192.168.9.1 (Voice VLAN) attached to VLAN 200.  This has all worked fine for a year until about a week ago, every 4 hours I can longer transit the routed interface.  Whats weird is I see NO other interruptions.  This switch is the default gateway for 3 other routed VLAN's and it passes traffic between them with no issues.  I also don't lose connectivity at all on my 200 VLAN.  So the swith ports are all passing traffic, but the routed interface seems to disappear.  Again, this is like clockwork, every 4 hours. 

Anyone have any thoughts?  There have been no changes to the network, everything just went started 7 days ago.  I have tested with additional hosts on additional switches and I see hte same behavior.  Whats weird, is I can continue to ping the VLAN interface from my data network side so it doesn't go down, just stops passing traffic.

Last bit of data I can throw at this is that my voicemail server showed an invalid ARP for default gateway on default gateway of the voice network during the outage period.  Lastly, I have rebooted the core and the voice concentration switch and the timing is still at 3:15, 7:15, 11:15 ... so the clock is still the same on when this drops.

Thanks in advance for helping me think through / troubleshoot this.  It be much easier if something actually went DOWN instead of just stopping working :P