Thin vessel (8 mm). WRC297 nozzle flex was used. Loads will shift/distribute to stiffer elements

Your nozzle circ stiffness is low (4588 Nm/deg (40609 in-lb/deg), Long is essentially rigid (unlikely) and probably WRC 297 is inaccurate.
_________________________
Bob Zimmerman, P.E.
Vice President of The Piping Stress International Association (The PSI)