That was always a thing with Falco in Smash 4, so this is nothing new. Falco can get grabbed out by Luigi, Naired by anyone with with a frame 3 Nair like Mario, Dr. Mario, Luigi, and Sheik, Rested by Jigglypuff, Dolphin Slashed by Marth and Lucina - Dolphin Slash has I-frames, right? -, jabbed out by Fox, Captain Falcon, and the like, etc. It doesn't help that compared to to other rapid jabs where the user extends a limb like how Fox kicks out or how Kirby's stubby arms become longer, Falco puts his hurtbox out in front while spinning with his arms slightly stretched. Of all the jabs in the game, Falco's is both the worst and best. Jab 1 and 2 are amazing as he swipes in front of him while moving forward, but rapid jab is horrible since his hurtbox is right there. Seriously wished Falco had a gentleman, a regular jab combo - they could just remove his rapid jab and make it as part of the animation before he does his rapid jab finisher -, or do something like make him partially invincible since it's really stupid how Falco gets hit between jab 2 and rapid jab or gets him during rapid jab while hitting people unlike Captain Falcon, Kirby, Little Mac, Rosalina, Palutena, or Fox. Hell, they could do something "special" and make it so Falco's the only character with an incomplete jab. Sort of like Samus's - hers is more of an issue of how slow jab 2 comes out -, but more like Fox's except Falco has to pick between tilts, Smashes, shield, grab, or another option while hitting jab again too soon will just result in Falco just standing there like an idiot.
Edit: The irony is that is that apparently, Falco can transition to rapid jab 1 frame faster than previously. Probably doesn't help at all...