The most common reason that using the @ and # symbols does not translate into actions that are recognized by our system is because students are copying and pasting content from another text editor into the Yellowdig Pin editor. The @ and # symbols, in particular, have to be typed into the Pin editor window to be recognized "on-the-fly" as you are typing. This prevents these and some other symbols from being incorrectly recognized if pasted in as part of a formula, for example.
The easiest fix for most symbol recognition and formatting issues is to compose your Pins entirely in Yellowdig's Pin editor, rather than copying and pasting. The editor has both an auto-save and manual save feature (available by clicking the 3-line "hamburger" to the left of the Post button at the bottom of the Pin editor). These functions should prevent you from losing work. If you want to then save your work outside of Yellowdig you could copy/paste from Yellowdig's editor.
What you see in terms of @mentions and #hashtags when you hit the post button is what will be rendered in your actual Pin or Comment, so the other solution is to manually find and replace instances of these after you've pasted them in. You will need to start a new name or word with the corresponding symbol and type/select the corresponding mention or hashtag, after which they will show up in the editor window with special formatting, indicating that the system has recognized them and will send the appropriate notifications* or log them with the appropriate hashtag.
*Due to privacy guidelines, most email notifications in Yellowdig are set to off by default. If @mentions are not resulting in other people being notified, please have them try checking and changing their notification settings.