Beta Testing is Underway - Not going Great

I invited a friend and his son to beta test the game 3 weeks ago (April 22). I then added a second wave of 4 beta testers on April 30, and a third wave (5 more) on May 7.

So far most of my testers are opening the app and playing around a bit when they first get invited, but don't come back. They've given me a few bug reports, which is helpful, but I'm concerned by the fact that they aren't engaging with the app other than the initial open. I'm taking this as a sign that something needs to change. Is it just the onboarding or the whole idea?

I've been following up with them via email. Today I asked a few of them what they need to bring them back into the app. Here's part of the email that I sent to a couple of them.

I wanted to follow up again. I noticed from the data, if I'm looking at the right account, that you haven't logged any reps since your initial trial run.

What do you think the app needs next to encourage people to log reps at least a few times per week?

Some possibilities:

1. More direction (tasks/objectives)
   2.Reminder notifications (your energy meter is full)
2. A better explanation of how to make progress?

What would work best for you?

Hopefully I get some good feedback from these emails.