I think tank sensors reliably work only 1 time, and that is the very first time. After that, anything goes. This is just the normal for every RV.
What happens, "stuff" clings to the sensors when you dump causing a false reading. It just that simple. Nothing wrong with the sensors or the electronics behind it.
I have found that dumping the tanks before traveling from one location to another, and then adding about 5 gallons of water to the tanks before traveling works very well to keep the sensors clean and operating the best.
So, before leaving your campground, dump your tanks completely. Flush the black tank if you have a tank flusher. After dumping add a few gallons of clean water back in the tank. I also add a couple ounces of Dawn Dishwashing liquid. Then hit the road.
The sloshing of the water will pulverize anything stuck to the sensors, and when you use them the next time, they will work pretty good.
My current camper is now 4 years old and I've been doing this since it was brand new. My sensors on all my tanks are still working. How accurate? Well, at least I know when they are full.
However, I have learned to NOT rely on the sensors or the read-out with the push buttons.
I can estimate my water usage and here's how I do it.
First, I never hook up to city water. I always fill my fresh water tank and pump water from there. Why? Because I don't trust pressure regulators and I don't trust campground water sources for constant steady pressure, especially when they tell you the average water pressure is 70 psi. I decided early with my current camper to never hook up to city. I fill my fresh tank. It's worked perfectly fine for us, and we don't mind hearing the water pump come on and off.
Now, using ONLY the fresh water tank, I know that tank holds 50 gallons of water. I have 3 other tanks, 2 grey and 1 black. All three of them are 30 gallon tanks.
We have just learned over the years, we can take 6 showers, and use the toilet for 2 days before that 50 gallons is gone. We do most of our cooking outside and washing dishes outside. The water used outside is harder to estimate usage, as it draws from the fresh water tank and depletes the 50 gallons. But definately, when the water pump begins to spit air, we know it's time to (1) add more water (2) dump the tanks. When camping, I dump the black and shower water grey every day. I use the shower water to back-wash into the black tank. Usually, it works out just perfect. My 32 gallon Barker blue tote is not quite full, full enough to over fill.
Between filling a 50 gallon fresh water tank, and dumping into a 32 gallon blue tote, it doesn't take long to just "know" when it's time to dump. Practice, time, and patience makes perfect.
Now, when we first got our current camper, I did hook up to city water, and several times fill the shower tank, enough water was standing in the shower pan around our feet. It's MUCH harder to estimate when attached to city water, especially if you travel from campground to campground where water pressure is different at every place.
These are my "tips" for the day.
Dump, flush, add water and a bit of laundry or dishwashing soap, go for a drive and sensors are almost always clean and work.
Over time, you will develop a 6th sense at your water usage and just "know" when it's time to dump.
When you return home ... you'll find yourself taking "Navy showers" almost all the time. Don't be surprised!