Try using 4.27+, in my experience it’s more stability version for AR (without some other bugs like in 5.0 and etc). But, for normal working, you must understand how engine and openXR works, because some little repair is normal for AR in ue4. Like “ON Lidar” or late update tracking in ios, some trouble when you open app after minimized or error in scheme startSession-stopSession-startSession in Android. For me 4.27+ is enough for Android, because this platform has very limited AR functionality and repaired by pair of crutches, compared to Apple. But for development AR in ios, we moved in swift.
With normal Swift support or the ability to use the actual ARkit functionality in UE, problem could be solved by community. Without this, you shouldn’t expect big breakthroughs in AR with obj-c.