My first frame had the seams or joins in the track also. You could butt them up against each other but like you said, the frame would settle a little and the join area would cause a slight bump in the tracks. There was an upgrade for my frame (B-Line) that was for continuous tracks. The only other solution was to permanently level and rigidize the frame by setting it on cabinet bases. Many people have changed out their pieced tracks with tile edging, closet door tracks, angle iron--anything that they could obtain that had an edge for the pulley type wheels to run on like train tracks.
Replacing the tracks with some type of continuous edging material or rigidizing the base of the frame would seem to be the only fix for your frame as well.
My new frame, a SuperQuilter ProFlex uses a different method as do the Hinterberg Frames--the wheels run on conduit not tracks.