So I'm not crazy/ have a defective phone!
I've noticed this a lot! Not entirely bad, as I only use the speaker while I shower, and those late night YouTube videos, but i caught on to that happening, only my second night of using the phone
Some issues of my own that I've come across:
Volume gets practically inaudable after like 50%, on speaker... A little weird. Some apps respond differently though to volume levels
Volume seems to change on its own when I'm playing music through the speakers. I'll be in the shower, music...