Are you talking about Level 1-4? 1-5 is not a level in the game, so I would guess you were referring to a specific stage in one of the levels, perhaps? The format for levels is CHAPTER-LEVEL, and each stage of a level is just referred to as Stage X.
Jumps should be registering as long as you're grounded to a surface, or wallclimbing/wallrunning. It might be the case that you're jumping either too early or too late, or there might be an issue with either the Player Movement or, worst case, an issue related to Unity's Input System. But without specific info, I can't really help too much, sorry!
What I would suggest is to practice jumping in the Sandbox level, and if you're still experiencing persistent issues with Jump inputs not registering, please do let us know! Thanks for giving the game a try!
