The fallback_dest typically completes in 40-45 seconds on my machine. Occasionally, the test times out with:
Increasing the test timeout from 60 to 240 seconds produces the same result but it takes a total of 280 seconds.
In all recorded failures the counters n_tx=0 and n_rx=0 are the same. The n_rel varies around 2800 (2799, 2816).
The most successful loops before a failure was 120. Usually it fails in around 10 loops.