big3d timeouts

We are experiencing intermittent big3d timeout errors from our GTM sync group. It seems that the GTM whose gtmd is selected to poll is okay, but the other GTMs in our sync group will report a bip3d timeout:

GTM2.ABC.LOCAL alert gmtd[12345]: 011a6006:1: SNMP_TRAP: VS /Common/website_vs (ip:port=192.168.1.100:443) (Server /Common/LTM1.ABC.LOCAL) state change green --> red ( Monitor /Common/bigip from /Common/GTM1.ABC.LOCAL : no reply from big3d: timed out)
GTM3.ABC.LOCAL alert gmtd[12345]: 011a6006:1: SNMP_TRAP: VS /Common/website_vs (ip:port=192.168.1.100:443) (Server /Common/LTM1.ABC.LOCAL) state change green --> red ( Monitor /Common/bigip from /Common/GTM1.ABC.LOCAL : no reply from big3d: timed out)
GTM4.ABC.LOCAL alert gmtd[12345]: 011a6006:1: SNMP_TRAP: VS /Common/website_vs (ip:port=192.168.1.100:443) (Server /Common/LTM1.ABC.LOCAL) state change green --> red ( Monitor /Common/bigip from /Common/GTM1.ABC.LOCAL : no reply from big3d: timed out)

The VS will remain in an down state on those GTMs until we trigger some kind of change like adding/removing a GTM generic host. But that might also trigger a big3d timeout on another VS. There doesn't seem to be any pattern into which VS result in big3d timeouts. It's not the same set of GTMs everytime either.

Our LTMs have discovery enabled (no delete) and there are about 1500 total VS discovered across 6 LTM pairs. The LTMs have Service Check disabled in the iQuery settings as we do not want our LTMs performing monitoring for the ~400 generic hosts. 

I looked at https://my.f5.com/manage/s/article/K52381445 to try and track down the reason for the big3d timeouts. The iQuery mesh looks good and I see packets incrementing between all BIG-IP devices. I enabled gtm.debugprobelogging and set the log.gtm.level to debug on all the GTMs and reproduced the big3d timeouts. It generated many 'probe to' and 'probe from' messages and I could see references to various VS in the events, but I found no reference to the name or IP address of the VS that timed out. I'm not sure if debug logging is working as expected because I searched for a VS that remained healthy for the 15 minutes I was running debugging and still found no reference to it.

Are there any recommendations to tracking down the underlying cause of the timeouts? I tried capturing the iQuery traffic to see what is happening on the wire but I was unable to decrypt it. I'm guessing mutual auth is preventing me from doing this. We are rather hesistant to start poking at configuration settings without getting a better idea of issue.