Lately, I was fabricated solid-state Ag/AgCl reference electrode with the help of AgCl nanoparticles as compound filling that surround 1 mm dia. silver wire in my vessel. I used two-electrode system with demin water as the tester solution to measure the potential of my electrode.

For first measurement, I found that the data varies between 200-300 mV (fixed potential of Ag/AgCl electrode is 222 mV) and I consider my reference electrode is working properly (as shown in the first video).

But after a few measurements, 3 or 4, the data is really really broken (as shown in the second one). I've tried change on different multimeter, but it's still same

What is possibly happening?