Hello, could you please tell us what the log is showing about the sync?
It could be easier for you just to track the last few lines on the log after you force/overwrite the configuration from the active or primary device to standby/secondary device.
At least this will help you to track the error.
About SYNC inconsistent i am not sure but that sounds to me like both conf files are different and in conflict (this can happens when both devices are managed at the same time and changed on the configuration are performed simultaneously.Just force conf as a said before and reply with the results.This will not impact at all your environment.
I am going to supposed that ASM sync is enabled. Right? if not do it, Security>Options>Application Security> Synchronization> and choose the device group.
Regards