Some users are reporting issues with Google Assistant reminders after the most recent update.
Adding reminders by voice or text still seems to work okay, with entries still appearing in the reminders list. However, users don’t receive notifications for them.
The problem also reportedly extends to the beta version of the Google app, but I wasn’t able to replicate the behaviour myself.
Further, some of the reports indicate Assistant is having other issues as well. One user noted that Assistant asked him if he was ready to save his reminder multiple times. Others have said Assistant sends them old reminders that they’ve already marked as done.
Currently, the only solution available looks to be uninstalling updates. Rolling back to version 9.0.5 should fix the problem for now.
Update 01/28/2019: Google is rolling out a server-side update that fixes the issue with notifications. Users experiencing the issue may receive several reminder notifications that they had missed before when the update hits their device.