If your snippets work everywhere except one application, there are two settings worth checking before assuming something is wrong.
Check #1: Your Expansion Preferences
Go to:
Preferences → Expansion
Check your Expand Snippet Groups setting.
If you want your snippets to work everywhere, make sure it’s set to:
When typing in all applications
If it’s set to All applications, except…, review the excluded applications to make sure the app you’re using isn’t on the list.
Check #2: Your Snippet Group Settings
Select the Snippet Group, then click the 
Gear (or right-click the group and choose Group Settings).
Look for:
Expand in
If you want the group to follow your global Preferences, make sure it’s set to:
Default (in Preferences)
If it’s set to All applications, except… or limited to specific applications, review those settings to confirm the application you’re using hasn’t been excluded.
Remember: Both of these settings work together. Even if your global Preferences allow expansion everywhere, an individual Snippet Group can still be limited to (or excluded from) certain applications.
Have you ever discovered a setting that made you say, “Wait… that’s why it wasn’t working!”? We’d love to hear your biggest TextExpander “aha!” moment.