Now, I won't pretend I know the reason precisely, but around here, we discontinued use of the old NE555 back in the early '80's, because of the system noise, specifically Vcc-to-Gnd noise. The CMOS inverter oscillators make very little noise at full voltage, but, as the Vcc drops, the noise margin is decreased, and the noise becomes significant with respect to Vcc. The stiffer (in amperes) the Vcc supply, the less significant the noise, but as people use CMOS, they expect to be able to "get by" with a less powerful supply, hence, the noise made by a component like the 555 as an oscillator becomes significant, unlike the days when even a small system had a 5-amp supply.

I remember transformers that weighed on the order of 15 kg providing the required 5-volt, 12-volt bipolar, and 15-volt bipolar supplies, along with a hefty 24 volts for the relays. The 78xx regulators had multiple pass-transistors, hefty crowbars, and fuses in the tens of amperes.

When your whole supply has only 200 mA, a bit of ground bounce becomes significant, particularly with respect to a 3-volt supply. Isn't that sufficient to provide the crosstalk between oscillators?

RE