What is the legal ruling on a group of women who prayed, led by one of them, after the Imam's voice from the upper floor of the mosque was cut off, and they could not see the Imam, then the voice returned in the lastركعة (unit of prayer), and they did not follow the Imam because they did not know their position in the prayer?

Their prayers are valid, and they are not required to repeat them. If the sound from the loudspeaker cuts off, the congregants complete the prayer individually or they put forward one of them to lead. They must wait before intending to pray individually, as the sound may return.

Indeed, early jurists mentioned a similar issue: if a congregation praying in nearby ships disperses due to wind, they pray individually or put forward one of them as an imam. If the ships return, they do not go back to follow the first imam.