black pill voltage instability fixed

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Recently I got WeAct Black Pill V3.0 Board with STM32F411CEU microcontroller.
While testing microcontroller peripherals, I noticed that processor voltage was unstable.
It was randomly switching between stable 3.30V down to approximately 3.1V. When near 3.1V, it was oscillating with small amplitude.
The voltage switching from 3.30V to 3.1V and back was happening at random times, typically in tens of seconds.   

This processor voltage is supplied by tiny LDO linear regulator identified as 4B2K on the top of the case.
LDO stability is known to be very sensitive to the ESR and capacitance of the capacitors at their output.

The capacitors of the WeAct board look tiny. I assume that they are made of very temperature unstable ceramics.
Decreased capacitance may cause LDO instability.
In an attempt to fix the instability, I connected tantalum capacitor between 3.3V and G pins next to the LDO. The capacitor is Sprague Series 293D 4.7uF, 10V.
The ESR of this capacitor was measured by DER DE-5000 to be 0.58 ohm at 100 kHz, while measured capacitance was 4.93uF.

After the capacitor was connected, the LDO output voltage remains very stable at 3.30V.