Hi - I had similar issue at first. I fixed by ensuring the phone was paired to the remote control first by WiFi (with the drone turned off). Then turning on the Spark, and it then connected to the remote and has been fine ever since.
Hope works for you.
I think I’d done something odd in the initial set up to try to connect direct to Phone when I always wanted to use the controller.
I heard somewhere that if you hold the power button down on the RC for 9 seconds it factory resets it maybe worth a try. Also I could not get my phone to pick it up first of all and that was because it was on 2.4ghz mode and my phone did not work on that frequency had to change it to 5.8ghz in djigo4 app. Hope some of that helps