had the same problem and was able to solve it:
I disassembled more or less the whole speaker (use the right screwdrivers, not to mess up the screws) following some youtube vids.
I found two problems for the buttons not working and solved them like this:
1) The flat cable connecting the buttons with the circuit board tends to slip out of its “gripper” on the PCB.
I slid it back in, closed the gripper and put a little tape on top
2) The Bluetooth button tends to get stuck, wich causes the power button not to work any more. To solve this I opened the ruber cover between PCB and outside cover. There is a white/transparent plastic piece attached below, that has the same function like a “rubber dome” in a keyboard. It has two little noses on its bottom to push on the buttons on the PCB (power and Bluetooth). I cut off a part of the bluetooths nose, to give the button on the PCB more space to come up again. Obviously dont cut off too much…
after reassembling everything works as it should again and Im happy.