I have the same issue with my Charge 4 and to me it seems like the button detached from the frame and collapsed deep into the housing. I can still use it, but have to press really hard with my thumb. I wonder if the button can collapse even further or if it is the end? The speaker is just a couple of weeks old and I don't want to disassemble for investigating/fixing it - I will just replace it at where I got it from showing them this thread, if needed…
Otherwise super happy with performance and SQ.