You´re welcome :-)
Actually back the problem - I honestly do not have an idea at hand. Did you ever try to remove the HA configuration and re-apply it? Did you already attempt to reboot both boxes (during a maintenance window) and see if the issue persists?
Did you already file an SR with support? The HA issues on MWG 6.x are sometimes pretty tricky to troubleshoot. Support has a so-called "HA" script, which collect all the information they require to look into a complete HA configuration and all of the associated logs. Right from the screenshots I cannot provide a more detailed answer than above.