I have a Macbook Pro and an iPhone5. At one point, I received messages in sync on both devices. Now, I get some messages on the Macbook and others only on the iPhone. What happened?
Associate your mobile number with your Apple ID, if you haven't already done so.
Sign out of iMessage on the Mac:
Messages ▹ Preferences ▹ Accounts ▹ Sign out
and on the iPhone:
Settings ▹ Messages ▹ Send & Receive ▹ Apple ID ▹ Sign out
Then, on the phone, tap
Use Your Apple ID for iMessage
Sign back into iMessage on both devices and test. If there's no change, you may have to wait for a change in network conditions.
Credit for this solution to ASC user SmittyLove and to Glenn Fleishman of tidbits.com.
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