are you using a animation blueprint to drive your animations? it could be a issue in the transition rules. Or you could have a input issue where you jump event is being triggered multiple times. along that line of thought your keyboard isnt sticking right? also is your cpu being overworked? I see you used the launch character tag, does that mean your using that node or are you using the jump node?
there are many things that could be causing an issue so if you could, please post a video or some screenshots of your blueprints that would help.
I was having a similar problem to this where my character was constantly jumping. I realised that I was launching my character even when my flying button was not being pressed. Here is what fixed it for me. I hope it can in some way help you.
