Apologies if this is a duplicate, but I can't find a bug report anywhere.

Steps to Reproduce:

1. Load a page in VisualEditor.
2. Edit something.
3. Disconnect internet.
4. Hit preview.
5. Get Error loading data from server: Failed to connect.
6. Reconnect internet.
7. Hit preview again.
8. Still get the cached Error loading data from server: Failed to connect.
9. Edit something else.
10. Hit preview again.
11. Preview succeeds as the cache is invalidated.