Documents being resharded have associated config.transactions updates communicated via standard MDB oplog fetching queries. Without RRFaM, the pre/post images for retryable find and modifies are stored in the oplog themselves and captured by these queries.
With RRFaM, those images are written elsewhere not yet known to resharding. Without any work, resharding while using RRFaM will lose the necessary data for retryable findAndModifies.
It's safe and correct to document that to reshard a collection, a user must first turn off RRFaM on every node in the sharded cluster prior to issuing a resharding command.
For this ticket, we aim to do better and have resharding be aware of the config.image_collection data and copy over the necessary items as needed.