  We report on the successful operation of a double phase Liquid Argon Large
Electron Multiplier Time Projection Chamber (LAr LEM-TPC) equipped with two
dimensional projective anodes with dimensions 10$\times$10 cm$^2$, and with a
maximum drift length of 21 cm. The anodes were manufactured for the first time
from a single multilayer printed circuit board (PCB). Various layouts of the
readout views have been tested and optimised. In addition, the ionisation
charge was efficiently extracted from the liquid to the gas phase with a single
grid instead of two previously. We studied the response and the gain of the
detector to cosmic muon tracks. To study long-term stability over several
weeks, we continuously operated the chamber at fixed electric field settings.
We reproducibly observe that after an initial decrease with a characteristic
time of $\tau\approx 1.6$ days, the observed gain is stable. In 46 days of
operation, a total of 14.6 million triggers have been collected at a stable
effective gain of $G_\infty\sim 15$ corresponding to a signal-to-noise ratio
$(S/N)\gtrsim 60$ for minimum ionising tracks. During the full period, eight
discharges across the LEM were observed. A maximum effective gain of 90 was
also observed, corresponding to a signal-to-noise ratio $(S/N)\gtrsim 400$ for
minimum ionising tracks, or $S/N\approx10$ for an energy deposition of 15 keV
on a single readout channel.
