Short answer
The reason is because of where they are located. FSAL resides in/near the TDRSS Zone of Exclusion, illustrated by the notation ZOE in the map below, bordered by the yellow line on the left and the green line on the right.
"Main Screen in the ISS Mission Control Center", by AGeekMom, CC BY 2.0
More detail
The ISS uses Ku-band communications to relay video to the ground stations via NASA's Tracking and Data Relay Satellite System. ISS uses satellites positioned in three different slots around the world to relay telemetry, voice, video, and commanding. These are located at longitudes of 46 degrees (TDRS E), 171 degrees (TDRS W), and 275 degrees (TDRS Z).
In the map above, you can see yellow, green, and blue lines outlining regions in orbit where those satellites are shadowed by the earth. The region marked ZOE happens to correspond to where TDRS Z is the only satellite in range. Why is this important? NASA often will not use TDRS Z during quiescent operations, for several reasons: 1) ISS is not the only customer of the TDRSS system (and it's not even the #1 priority customer), and 2) data relay through TDRS Z is not as good as data relay through TDRS E and W (both of which are within range of the primary TDRSS ground station at White Sands, New Mexico).
In general, TDRS Z is only activated for ISS when station is undergoing what they call "TDRSS Critical" ops. These would be things like visiting vehicle ops, EVAs, and the like. Otherwise, the roughly 5-10 minute loss of signal is acceptable and even provides flight controllers an opportunity to take a quick break while their console displays go blank.