I think this 5 is SL_POSITIONAL_TRACKING_STATE_UNAVAILABLE, which was officially added in 4.1
See the enum from here: Blaming zed-c-api/include/sl/c_api/types_c.h at main · stereolabs/zed-c-api · GitHub
enum SL_POSITIONAL_TRACKING_STATE {
SL_POSITIONAL_TRACKING_STATE_SEARCHING, /**< \warn DEPRECATED: This state is no longer in use.*/
SL_POSITIONAL_TRACKING_STATE_OK, /**< The positional tracking is working normally.*/
SL_POSITIONAL_TRACKING_STATE_OFF, /**< The positional tracking is not enabled.*/
SL_POSITIONAL_TRACKING_STATE_FPS_TOO_LOW, /**< The effective FPS is too low to give proper results for motion tracking.\n Consider using performance parameters (\ref SL_DEPTH_MODE_PERFORMANCE, low camera resolution (\ref SL_RESOLUTION_VGA / \ref SL_RESOLUTION_SVGA or \ref SL_RESOLUTION_HD720).*/
SL_POSITIONAL_TRACKING_STATE_SEARCHING_FLOOR_PLANE, /**< The camera is searching for the floor plane to locate itself with respect to it.\n The \ref SL_REFERENCE_FRAME_WORLD will be set afterward.*/
SL_POSITIONAL_TRACKING_STATE_UNAVAILABLE, /**< The tracking module was unable to perform tracking from the previous frame to the current frame. */
};