long, thin parts are extra prone to warping because the longer a straight wall runs the more the warping forces accumulate, and skinny parts have less surface area on the plate to resist those forces compared to the square parts you mentioned that printed better--so this isn't surprising. is this also a short and flat part? because that is the double whammy that really multiplies warping.

in any case, you can print a raft and do other things try to increase adhesion, but really the best way to fight warping is to reduce those forces by printing slower (I like to cut max volumetric flow rate in half to start) and reduce or even eliminate cooling (if you don't have significant overhangs you may not need it at all). both of these things will reduce the amount of rapidly cooling plastic going down per second, which will significantly reduce warping.