gosrox I just tried this app and it didn't seem to double my step count after a reboot. However it did feel fairly inconsistent. Regardless of whether there's been a regression here (I'm personally unsure as I haven't used this app before), I feel like I have to note that you probably shouldn't be using an app that's out of date.
Not only has it not had an update for years, but it's also stuck on target SDK 26. That's ancient. For context, we're currently at SDK 33. The SDK level brings privacy and security improvements which are often very substantial, and you should try your best to use apps which keep up with that.