Hi there Teach2544,
Is this happening with the built-in Mail app or with the third-party Gmail app? If this is happening with Mail, try removing the account and adding it again:
Remove your email account and set it up again
1. On your computer, sign in to your email provider’s website. Make sure that all of your email is there or make sure that your email is saved somewhere other than your device.
2. On your device, go to Settings > Mail, then tap Accounts.
3. Tap the email account that you want to remove.
4. Tap Delete Account.
5. Add your account again.
You'll find those steps here: If you can't receive email on your iPhone, iPad, or iPod touch - Apple Support
If this is happening with the Gmail app, work through the steps in this support article to see if they resolve the issue, including contacting the app developer: If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support
Take care.