I have an old Ender 3 printer. I have let it sit for a year without anything to print. Nothing major has happened to it like falling or setting things on the printer.
It has an old BLTouch. I set up the BLTouch in this way:
Auto home after setting Z-offset to zero
Move Z-axis to what it thinks is zero.
Move the Z-axis down to a piece of paper until it barely grips (or up sometimes) to compensate for offset.
Copy the offset number positive or negative to the offset. It's also worth noting that my offset has been positive usually negative. Also it's nearly double what it was last time I did this.
Then I start a print which includes an auto-home.
The magic happens now as the Z-axis rides nearly 3-5 mm above the surface of the printer bed. I have no idea why.
It might also be worth noting this printer is out of shape.