Default filters keep out new images for a short amount of time in case of mistagging, to prevent people from seeing content they shouldn't. It's currently set to 10 minutes, for the beta it might still be overkill but in the future it might not be enough. We do not know what volume of activity to expect or how quick mistags will be fixed.
This box that shows up right after an upload will soon be updated to include the same explanation. Hopefully it won't be easy to miss.
If you want to remove this condition in your own filter and don't know how, erase the text in thet last box when editing a filter, titled "Complex Hide Filter", or edit it to your own preferences.
Feel free to use this post for feedback or for further questions on filters.