Few days ago a problem appeared on my Focus

Both motor and car speed  indicators drop to zero, LCD mileage indicator
shows dash lines (------) instead of  kilometers and a second after the
orange motor pilot lamp lit. Then a few seconds or minutes later indicators
kick back to normal and the problem disappears.

I don't feel any influence on engine behaviour and the failure seems
absolutely random not depending on engine or car speed or any electrical
device switching.

Sometimes other pilot lamps lit (e.g. battery).

Ford Service made already a computer check while the problem was not present
(no luck) and ddn't find any fault.
The only logged alarm was "positive of fuel indicator level sensor shorted
to ground" but the fuel indicator is the only which never drops during the
failure.

Has anybody as an idea about this strange problem?

Gian Piero