QUICK ANSWER
Open the app before assuming there is no error.
iRobot specifically says a j-series robot that stops with no lights or visible message should first be checked in the app, then resumed or rebooted.

INTERACTIVE DIAGNOSIS
Why did the j7 stop?
STEP 1 OF 2
Does the app show an error or warning?
The robot itself may not show the full reason.
Repeated stopping is not a reason to bypass sensors
Do not tape over cliff sensors or defeat safety sensing to keep the robot moving.