I tried running the same command on a Raspberry Pi 3 with a 1 Wire Pi Plus installed and it returned found 100 times so it looks like there is a problem with the communication between your Raspberry Pi and 1 Wire board.
Please can you try checking all of the solder joints on the GPIO header, 2 pin jumper and RJ12 connector to make sure there are no dry joints or solder bridges? An intermittent fault like this where the 1 Wire board it is detected some of the time would suggest a mechanical or software issue.
If you have a spare SD card it may be worth trying a clean install of Raspbian Linux to rule out any problems with the version you are currently using.
If the problem still persists after that then it could be a fault with the 1 Wire Pi Plus in which case I will send you a replacement.