Sometimes the plugin isn't running when something good happens. The submit page lets you record it yourself.
During events, manual submissions usually don't score instantly: most events are set to hold anything that didn't come from the plugin in a pending review queue, and an event admin confirms it before points are awarded. If your submission shows as pending, that's working as intended — it will count as soon as an admin approves it. (Event organizers can change this under the event's submission policy.)
Manual submission is for one-offs — the plugin is always preferred because it's automatic and verified as you play. If you find yourself manually submitting often, check the plugin's settings to make sure the category is enabled.