Hardware Syncookie issue after upgrading to 12.1.2 HF1

I recently upgraded my vcmp HA guests from 11.6.1 to 12.1.2 HF1 and a few days after the upgrade, we started having a lot of connectivity issues to our Sql servers. I opened an F5 case and was told that the fastl4 profile being used on my routing virtual server (for tcp traffic) had "hardware syncookie", "loose initiate" and "loose close" enabled. According to K14779, these should not be enabled at the same time. Once I disabled my hardware syncookie setting in my fastl4 profile, everything was fine. I was seeing tons (3000+) of "hardware syncookie threshold exceeded" log entries post upgrade. Prior to the upgrade, I was probably only seeing between 20-30 in an ltm log.

 

What baffles me is why was this not a problem prior to the upgrade when I was running on ver 11.6.1? The fastl4 profile settings were exactly the same pre/post upgrade. The traffic patterns did not change. I'm just curious if anyone else experienced something like this. I would like to get to the root cause of this outage but it's not looking like we will.

 

thanks