Solution:
UE has only 32 slots for audio sounds to play simultaneously.
In my 3 sound notifies:
Firing
Pulling the forend
Pushing the forend
I used Metasounds which start playing on the Notify and every time take 1 of the 32 audio slots.
Meaning every time a Notify triggers an SFX to play, 1 additional sound slot is being used, until it reaches the maximum amount of 32 sound slots. Then the sounds start to disappear.
I allocated 2 sounds slots for the shot SFX.
1 slot for pull SFX and 1 slot for push SFX.
I added the logic for this in ABP for the individual weapons and a general logic in C++ for all weapons.
Once I equip my weapon, X amount of audio slots (audio components) are spawned for the particular gun SFXs.
An SFX that plays has a maximum lifetime of up to 2 seconds. Then I stop it, so it does not take CPU resources.
I used this console command to figure it out: au.debug.soundwaves 1
Somehow, for me, it only works after I detach from my player with F8 and then quickly type it in.