Can you ground the dielectric of a capacitor?
Soil, and ground is a hotbed of electrical signals. Metals, oxides and other conducting materials react with fluids and generate currents by galvanic processes. Currents that can be large enough to 'eat away' railroad hardware (which is why, in some areas, large zinc or other metals are buried to main the 'hardware' intact...

I doubt you will be able to measure capacitance reliably in soil, unless in a protected environment, isolated from the rest of the ground.

I suspect that your capacitance meter gave up, because of the 'bad quality' of the ground capacitor. After all, the ground also acts as a resistor, in parallel with the capacitor you're trying to measure.

I doubt shrink sleeve will protect your electrodes from conducting. Maybe covering a bottle on the inside with foil could work. But still, the capacitance will still effectively be a C in parallel with an R, and will be very difficult to measure.

Also, imagine that the capacitance between your electrodes, will be just a couple of pF, compared to all the capacitance to the rest of the 'earth'.

The capacitance in the glass will work, because the resistance is very high. Put in some salt, and you'll see how C varies! And then you'll probably be measuring the capacitance of the shrink sleeve, not the water.

Try measuring R directly - at least then there are no oscillators involved, as used in measuring capacitors.