If your pH was really 7.75, I think you would see a lot more in the way of deficiency/lockout symptoms, so I'm not going to tell you to try to adjust pH.
I'm sure the soil where you planted that instrument is wet, but the soil along the edges of the pot are not. Try and make sure that soil along the sides of the pot get moistened, too. But then back off on watering for several days, until it's close to dry. You don't need an instrument to tell you when soil is wet or dry, you can trust your sense of touch and the weight of the pot.