It seems the information coming from your clock is not sufficient to be considered sync, the Aeros must read sync ON to behave as it should when following a clock.
Other users have reported similar mysterious sync issues but we have not yet found a clear answer why some devices seem to work fine while others are intermittently working or not at all. I would fumble with your clock’s settings if it has any and assure you are on latest firmware 4.3.1
We will be keeping an eye on this. What is the name of the external MIDI clock you are using?