What you’re saying makes perfect sense to me. Someone is making changes to your settings, without explaining what they are changing and why. I’ve actually talked to many photographers at various times, assuming they knew more than me, only to find out they just had more money to buy more expensive equipment. If I am asked by someone if I can help them with settings on their camera, I usually ask them a few questions to determine more clearly what they understand, help them find where to change the settings I recommend, explain why I suggest the change, and tell them how to change it back. Only some of the information likely sticks, but it’s better than changing settings on someone who doesn’t understand them and not providing any real help. Like
@DRwyoming mentioned, the three main pieces of the the camera you need to understand first is Shutter, Aperture, ISO (which is what the book I recommended explains). These three settings happen to be the same for every camera you pick up. Shooting manual might help you learn the camera more, but will be more frustrating as well. Once you got this down, that is when you will see the improvements from the other books and videos mentioned.
Given your example of switching to Aperture Priority and getting soft images is most likely A result of the camera choosing a shutter speed too slow to achieve a sharp image given the subject moving or camera movement. The auto ISO function allows you to set minimum shutter speeds that could help with this.