Sortd currently only works when Gmail is running in its Default mode, so its possible that if you have Gmail labs (or other Chrome Extensions) installed that they will clash with Sortd, in such away that the Gmail Toolbar will disappear from time to time. Please see this link for more details on the best configuration to run Gmail as What Gmail options/settings/configuration does Sortd work with? (Sortd may work in other configurations but it is not officially supported yet. We do hope to include other configurations in the future).
To test if Gmail Labs are interfering with Sortd, please disable the labs and refresh to see if Sortd starts working. You can always enable the labs again.
To test if a Chrome Extension is interfering with Sortd, please create a new Chrome Profile and install Sortd again (you won't need an invite code if you use the same email address).
If you find that the problem is caused by neither labs or extensions please get in touch and we will investigate further.