As JBL has new products out, as well as Connect Plus… and I had the same problem with Android… I don’t know how relevant or helpful this will be.
With the above being said…. I had the same problem with my Galaxy S6, two Charge 3’s and the JBL Connect App. The phone and speakers would pair together and work just fine, but the Connect App would not go past the discovery screen and kept advising me how to pair a speaker.
Despite powering the phone and speakers on and off, as well as removing and renewing the Bluetooth pairing of the speakers, I could not get JBL Connect to recognize the Charge 3’s.
My final attempt to get JBL Connect to work was to uninstall/reinstall the app, reboot the phone and factory reset the Charge 3’s.
From there, I powered up the Galaxy S6, made sure the Bluetooth was off and opened the JBL Connect app. When it prompted me to turn on the Bluetooth, I used the app to turn it on. Then I powered up one Charge 3 and paired it while the app was on… and the app recognized it immediately. When the second Charge 3 was powered up and paired with the first, it showed up immediately on the Connect App.
So far, the app and speakers have been working fine in both stereo and party mode through the JBL App, whenever I use it.
Hope this helps someone.
One thing I’ve learned after writing the above answer
I never updated the firmware on my Charge 3’s to Connect Plus and beyond.
My Charge 3’s are firmware 3.9. You find this by powering on the speaker then pressing the connect and volume down buttons. A voice will tell you your current firmware version.
When I updated the JBL Connect App on my Galaxy S6 beyond 4.1.199 I had the connection issues all over again.
As I’m fine with the original Charge 3 firmware and sound, I reloaded 4.1.199 into the Galaxy and it has worked perfectly.
I have JBL Connect 4.7.8 on an Ipad and it struggles, but eventually will connect the pair of Charge 3’s after several to many attempts.
So, if you have no plans to upgrade older JBL speakers to Connect Plus, you may want to stay with JBL Connect 4.1.199.
If you have upgraded your firmware to Connect Plus and newer versions of the Connect App, I don’t know how much this post will help.