Sortd works best with the default Gmail options enabled. 

If the Inbox type is anything other than "Default", the "Preview" lab or the "Multiple Inboxes" lab is installed Sortd may not work correctly and may clash with Gmail. Other labs may or may not cause problems depending one what changes they make to Gmail.

Sortd may not preview the correct email message if "Conversation View" is turned off. (Ensure that you turn Conversation View off in Sortd as well if you choose to use Sortd with "Conversation View" off). See here for more information.

Generally Sortd Fullscreen will work fine but the Sidebar and Sortd Add task button(s) may not work correctly and there may be other side effects in Gmail itself.

Certain other Chrome Extensions in Gmail may also conflict with Sortd.