When a new file is pushed to the repository, it is not accessible from the Source view. It will show "Hmm...can't find that one".
If you perform a hard refresh (clear cache) on the page, the issue is resolved. However, the issue will reccur on the next push.
Disabling the new source browser beta feature will solve this issue.
- Navigate to Bitbucket Settings and click Labs
- Look for the feature "New source browser experience"
- Disable the feature by clicking on the slider
- Browser your file once again and it should no longer show that error.