Check your composition dispaly settings in the relevant flyout menu and the global preferences (show bounding box and al lthat stuff)
Sorry I dont quite know where those settings options are. Could you please send a screenshot of the location those settings are.
Comp settings: cmd-k (mac) / ctl-k (win).
Preferences: Edit > Preferences.
Removing the bounding box got rid of the lines outside the frame but the random white light are still rendering in the final comp.