If the rewards are working on another device, that tells me there's something up with your original device. Considering the original device you reported is on Android 7 and this other device is Android 9, that could have something to do with it, but I can't say for certain what the cause is. The Ads services gets updated from time, so perhaps there's a conflict with older Android versions. I'll check with our engineering team to see if that's a possibility.