We've run into a few of these types of errors as administrators, both with SSL certificate work and Access Policy Manager changes. Based on our experience the root cause is making a change on one of the devices, then removing the change, then making the change again using the same name. Because the name was the same, yet it tied to some internal identifier, there was an unreconcilable conflict and the sync could not resolve it. I found the error by doing a diff on the bigip.conf of the two devices.
I would suggest you copy the bigip.conf file from both devices, perform a diff on the two files and compare line 6194 to see (a) what may be different and or (b) if that reflects a recent change you made on one of the devices, remove that change, attempt to sync and if successful, re-add the change and sync again.