Mac Messages Does Not Catch Up On Old Texts From iPhone After Power Up

It used to be the case when I turned on my Mac that the Messages app, once launched, would backfill with the texts I got on my iPhone while the Mac was turned off. This would take a few minutes but always happened. Now it doesn't do that anymore, and any iPhone texts are missing from my Mac which makes searching for old messages harder as I have to do it on my phone. What caused this and how can I fix it?