iMessages no longer mirrored on iPhone when phone is unavailable (and other device isn't)

The usually behavior for iMessages has always been (or always seemed to be striving towards) to mirror messages, even after they have been received by another device.

For instance, if my Macbook is turned off, and I receive iMessages on my phone, those messages will then be added in bulk next time I turn my Macbook on.

I like this behavior.

However after a recent iOS update (I can't pinpoint which one), this behavior has stopped being the case on the iPhone.

For instance, when I go to sleep, I put my iPhone on airplane mode - but my Macbook stays on in my office. During my sleep, if it receives messages, these will never make it to my iPhone, even after it is taken off airplane mode. This contrasts with prior behavior (before, when I woke up and turned airplane mode off, I would receive all messages that had been sent while I was asleep).

Has anybody notices this behavior? Is there something to do about it? If it's a bug, how I can best report it?