The FMC does occasionally have difficulty in computing an abeam waypoint exactly spot on the new direct track and may give your direct track a few degrees dogleg, especially when the turn to the new direct route is more pronounced, or has a strong wind input, or involves multiple waypoints the greater the dogleg off to an abeam waypoint. Since your ATC clearance is direct the new waypoint and not an abeam point, try reselecting direct again, and then reselect abeam points it will fine tune the track and remove the abeam doglegs