NewBee - unknown "possible" memory leak?

The data logger program (above) does not even use A10?

No, but when USB is unplugged, Espruino automatically switches the console over to use it. I just tried randomly poking the board around A10 and memory usage rose - it could be the problem.

Please could you look at Serial1.available() and see if it reads nonzero? If you then type Serial1.read() the data will be read out of the buffer and memory usage will drop.

The buffer for Serial1 is 'only' 256 bytes or so so it won't ever stop your code from working. I'll see if I can do something about it though - perhaps by not storing the data unless someone has previously called Serial1.read/available