After investigating BF-23456 the following hypothesis has been developed:

There is an interaction between the RSM and the ShardRegistry (most likely due to a HostUnreachable error) that temporarily prevents requests to the shard registry to be successful, making the ARS to return shard not found. However, the exact scenario haven't been determined, so, in order to confirm or refine the hypothesis, we need more information from the logs, and, due to the fact that the problem has not been reproduced locally, the best idea for now is to increase the log level of the resharding_coordinator_recovers_abort_decision.js test and wait for the next failure.