I reversed the loads due to this Wrong eigenvalue calculation since v2.16 and get 0.98 (ccx v2.20 spooles)
running your file directly in v2.20 with spooles I got 2.18 (let me know if in abaqus the buckling factor was positive or negative)
What is clear is the difference in location that might be attributed maybe to the load coupling behaviour or the knots overstiffening the shells in ccx at the intersection of spars/skins