@DarioGangi Just tried following your steps – I was able to repro the jittering issue similar to the one in OP using 5.4.2 so I think you’re right, we are all on the same page.
Doing more investigation into both the third person sample and my own 2D project, I found that disabling “Do Collision Test” on the spring arm component gets rid of the issue! Not ideal but at least for my case I am fine disabling this since I don’t rely on the spring arm component very much.
Very strangely, the issue is present even if there isn’t a camera component – in my 2D game, the camera exists on a separate actor blueprint. But if I simply add a spring arm component to my player character (without any camera or anything attached/referencing it) I start to get the jittering in packaged builds. @Jon.Cain maybe this is a place to investigate?