Those soil pH probes are not always the most accurate -- not because of their ability to measure pH but the context of a physical medium with varying moisture content. Evaporation will cause pH to get more extreme (whichever side of 7 it was on). The volume is in the denominator...
it's just a much messier reading that measuring pH in a liquid that isn't absorbed into a solid.
so, if you are just starting, i'd focus more on health of the plant before using this to preemptively fix anything... familiarity will be needed to properly use what the soil ph probe tells you... you will have to learn what is a normal ebb and flow and what looks weird and requires a reaction by you.
if the plant is growing fine and looks fine, it's fine. You'll have to learn what to expect from your probe's reading in order to interpret it properly in future.
ph-balance whatever water you add... soils that start drifting and doing wild shit are usually just poorly constitued soils... try a different brand.