I know this post is 5 years old, but this problem is still cropping up from time to time with no explanation. Specifically, myself and others have an issue with a large packet length of 1410, with a threshold of 1406. Unfortunately, you can't change the MTU because the maximum is 1406. This doesn't even make sense.
I did find one possibility. A troubleshooting article showing the ASA transmitting packets that exceeded the MTU could be fixed by running:
Login to the FXOS chassis manager.
Direct your browser to https://hostname/, and log-in using the user-name and password.
Go to Help > About and check the current version:
Check the current version availa...
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...