Two guesses: Ones is that the 2000 ms. delay after Cellular.on() for some reason is not long enough for the modem to turn on. Or maybe it's turn turn off delay. Just for testing, try setting the on and off delays to 15000 and see if that solves the problem.
Also, measuring the current can be tricky, depending on your meter. With many meters, using the nA or uA setting doesn’t provide enough current to successfully allow the cellular modem to turn on, so it can’t be turned off. This post discusses this: