When a shard is to be snapshotted, we acquire a store ref (wrapped in an index commit) and then enqueue the shard snapshot task for execution by the repository:

https://github.com/elastic/elasticsearch/blob/b124763772748d8993911e4a7ba94b17472a9539/server/src/main/java/org/elasticsearch/snapshots/SnapshotShardsService.java#L369-L384

If the shard is closed while its snapshot is in the queue then it looks like we do not release the store ref promptly. Instead, we keep hold of it until it reaches the front of the queue, which could be many minutes later. During this time the shard cannot fully shut down and release the shard lock, leading to a `ShardLockObtainFailedException` being thrown on attempts to reinitialise the shard.
server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java
"[{}] waiting  ing  of repository metadata generation in cluster state",
                    metadata.name()
                );
                repoDataInitialized.addListener(listener);
            }
        }
    }
    /**
     * Deduplicator that deduplicates the physical loading of {@link RepositoryData} from the repositories' underlying storage.
     */
    private final SingleResultDeduplicator<RepositoryData> repoDataLoadDeduplicator;
    private void doGetRepositoryData(ActionListener<RepositoryData> listener) {
        // 
        // 
        // 
        long lastFailedGeneration = RepositoryData.UNKNOWN_REPO_GEN;
        while (true) {
            final long genToLoad;
            if (bestEftConsistency) {
                // 
                // 
                final long generation;
                try {
                    generation = latestIndexBlobId();
                } catch (Exception e) {
                    listener.onFailure(
                        new RepositoryException(metadata.name(), "Could not determine repository generation from root blobs", e)
                    );
                    return;
                }