Typical reasons an auto-reverser does not work or stops working is that there is that
a) One of the gaps closes due to rail movement;
b) There is a poor electrical connection to rails on one or both sides of the gaps so that a 'good' short circuit current pulse is not created, as is needed to cause the AR unit to trip. The AR unit needs to be fed directly from the main DCC distribution bus, not from rail attachments adjacent to the gaps.;
c) The AR unit needs a larger pulse of current to trigger than can be delivered by the booster;
d) The AR section and mainline tracks are powered from different booster districts [requires a good booster common connection]
e) The AR unit is powered from the load side of an electronic circuit breaker that trips first [re-read b) ]
f) One attempts to use a Frog-Juicer or inferior AR unit that does not flip the polarity of both rails when only one side sees the current pulse.
g) There is a poor electrical connection of pickup bonding wires between loco wheels that limits the magnitude of short circuit current pulse need to trip the AR unit. The booster may trip first on a timed overload. [similar to b) and c) ]