I did two set of measurements with the new coated samples from Montreal. I reshuffled the position in the two measurements. In both cases, the measurement being performed in bay 4 was bad, in the sense that it was very hard to see excited modes. Since the two measurements were carried out with two different disks, it's clear it is a problem with that setup.

SOLVED: there was a connection problem for the DAC output signal controlling the switch

REALLY SOLVED: it was not a cabling issue. The power supply for the switching box had the current limiter on: when all four switches are closed, the box drain about 270mA, which is more than the limit of 250mA. Therefore the power supply voltage dropped and only three switches were actually closed. I switched the power supply to 500mA range and maxed the current limit. Now all four switches are working properly