Basic Fixes:

• Restart the Reminders app: If the Reminders app runs into unexpected glitches or bugs, it might not work as expected on your iPhone. When this happens, force the Reminders app to close from running in the background. Then, restart the app to see if this fixes the issue.
• Turn off DND: DND stops your iPhone from notifying you about other things. This can block the Reminders app from sending you reminders. So, when not required, you can turn off DND on your iPhone. 
• Check for iOS Updates: Software bugs might cause the Reminders app not to work properly. To fix it, an update should be timely released by Apple. Open the Settings app and manually check and install the latest software updates. 

Fix 1: Create a Time-Based Reminder

Making the reminder time-based ensures you get important reminders at the set time and date. Additionally, users on Reddit and the Apple Support Community also mentioned making your reminders time-based helps fix the Reminders not working issue. Follow the below steps to do it.

Step 1: Open the Reminders app and tap on New Reminder. Set the title and tap on Details.

Step 2: Turn on the toggle for Date and Time. Then, tap on Date.

Step 3: Select the relevant date for your reminder and tap on Time.

Step 4: Set the relevant time for your reminder. Confirm the reminder details and tap on Add.

This will create your time-based reminder in the Reminders app on your iPhone. You can also check our article to learn more about setting Reminders with alerts on your iPhone.

Fix 2: Check iCloud Settings

For the Reminders app to work properly, it must be enabled within the iCloud settings on your device. If you’re unsure about it, you can open the iCloud settings and have a look. Here’s how.

Step 1: Open Settings and tap on your name. Tap on iCloud.

Step 2: Tap on Show All. Ensure the toggle for Reminders is enabled.

Fix 3: Check Reminders App Notification Settings

If the Reminders app notifications are disabled or the notification tone is set to a quiet tone, it might cause the reminders to not show in the notifications panel or make them inaudible. To ensure this doesn’t happen, check the Notification settings for the Reminders app on your iPhone. Here’s how to do it.

Step 1: Open Settings and tap on Reminders. Tap on Notifications.

Step 2: Turn off the toggle for Allow Notifications. Wait a while and turn the Allow Notifications toggle on.

Step 3: Tap on Sounds and select a loud notification sound for the Reminders app.

Also Read: How to fix Apple Reminders not sending notifications

Fix 4: Remove the Reminders App Widget

The Reminders app widget can cause issues if the Reminders app widget is not working or updating properly. To rectify this, you can remove the Reminders app widget and instead use the Reminders app for a while. Here’s how to do it.

Step 1: Long-press the Reminders app widget and tap on Remove Widget. Tap on Remove.

Also Read: How to fix widgets not working or updating on iPhone

Fix 5: Disable Scheduled Summary

Scheduled Summary decides which notifications are important and batches the others for being delivered later. This can stop important reminder notifications from being displayed on your iPhone at the set time. In this case, you can disable Scheduled Summary and check again. Follow the below steps to do it.

Step 1: Open Settings and tap on Notifications.

Step 2: Select Scheduled Summary and turn off the Scheduled Summary toggle.