It seems like you have two separate problems: one with detecting beacons with the Estimote app, and one in your own app. These are usually unrelated: the Estimote app uses a different detection mechanism than the Estimote Proximity SDK which you embed into your own app. (I assume you use the Estimote Proximity SDK?)
For the Estimote app: so the beacons are sometimes detected, but sometimes not? That sounds like some problem with the smartphone maybe, what device are you using? Could you try with another Android device, and maybe with an iPhone and the Estimote iOS app? This will help us narrow down where the problem might be. (The Estimote Android app, or your particular Android device, etc.)
For your own app: same question I guess, do you sometimes detect the beacons and sometimes don’t? Can you maybe share your code, and also, if you’re using the Proximity SDK, make sure that the beacons are tagged correctly and have Estimote Monitoring enabled?