i had a theory a while ago, but didn't think it was worth anything since there were better sounding ones at the time, but if the thargoids are a insectoid species then they will probably have a hive mind. and a hive mind needs a queen which means somewhere out there is one or more queens, and also don't forget there could be bigger ships out there waiting for the second invasion.
which brings me to my theory of the attacks on fleets and capital ships, i honestly believe that the interceptors are basically cleaning up after the attacks picking up salvage and prisoners. but the what if the attack is not done by the interceptors but a capital size ship that jumps in attacks then jumps out leaving the interceptors to search for valuables and prisoner, because lets face facts interceptors are not exactly capital ship killers. to be honest i hope i am right, but i probably wrong