There is no way to change all audio levels in your project -- or even on a single track -- at the same time in Premiere Elements.
I'm not sure what's going on with the clip that's giving your trouble. Is it a WAV file or some other format? Have you tried deleting it from your timeline and re-adding it?
Also had this problem occasionally, randomly in various clips, and unable to find a reason for it.
If you use the level adjustment panel (upper right) you can adjust the level there along with all the other keyframes, both audio and video.
If I reposition the audio level bar, on the audio timeline, it resets the level in the selected clip.
In the situation I describe I was able t move the bar up on the first three clips, but when I tried to move the bar on the fourth selected clip it snapped back to it's original position.
I don't understand why it stops working after three clips.
Thanks for that suggestion. I went back to my video and ran that option and it worked; it's somesomewhat more complicated, technically; and more time consuming. But it does work.
I just don't understand why the down and dirty method stops working after a few clips.