Hello,
I bought my Extreme in October of 2017, after fully charging the unit I paired it up with my phone and took off for a ride on the UTV, about 30 min into the ride we began to have this issue you're explaining. We literally spent another 30 min trying to get the unit paired back up with my Samsung Galaxy 8 so we could enjoy some music, after the frustration started setting in we decided to pair it up with my friends IPhone 5 and off we went until about 10 min in the IPhone disconnected! We pulled over started looking at phone settings thinking it might be in the settings, decided that we would clear all Bluetooth paired history in the phone seems it had been paired with a few devices over the years! It worked... we spent the remainder of the day enjoying music. Now what I ended up doing to get my fancy new Galaxy8 to work was a little more time consuming. Once I was home I continued to have problems with the pairing of these 2 devices... seems that the 2 pieces of technology didn't like each other I was about to give up and setup the return with Ebay seems it was a brand new JBL Extreme other than the one day I got to enjoy someone else's playlist. I researched for a couple of hours reading lists of peoples complaints about how unsatisfied they all were with Harmon/JBL until I came across someone's post saying to hard reset the Extreme by holding down the pairing button & volume+ button at the same time. Once I did this the unit wouldn't turn back on so I unplugged the unit from its 110v connection and reconnected the 110v cord into the wall, had to push the power button many times until the unit decided to turn on. I haven't had any problems with it unpairing from my Galaxy8 since going thru all this and I have also unplugged it and ran it on battery power to see if the problem would come back! Hopefully my story will help you and others enjoy their expensive purchase of their fancy new JBL speaker!
Best Regards,
Tony