The transport drives itself toward the current base as stormtroopers surround it, trying to make the droid they can see stop. Finally the hover mechanism is targeted and the it stops.

By that time, Cassian has made his way about halfway to the his extraction point, he gets Hera's comm and responds with taps on his. Another squad passes him and he waits against a wall until they pass, ducking into an alley to use the Imperial comm to say in a breathless voice, "Some of those old droids are loose. I didn't know this many were still working."

Once he sees the patrols speed up, then he continues on.