Tank indicator...

Hello, friends.
After very long service life (second car) the tank indicator does not work. Tank content 3/4 full, display zero !
Briefly rolled up and fully braked, in the hope, if floats exist, this dissolves, without results.

Then after a short ride, as if by ghost hand, the ad is back there,

After a further 2-3 months of service life, the same scenario again.

Everything I have found on the subject here has been disheartened and rattled, but not a concrete, recreable hint to the question put.

So please just expert hints - thank you.
Type D2, A8L,4,2 / 2000

Greetings steals