"Maximum normal shards open " indicates that your target Elasticsearch cluster has hit its maximum shard limit as calculated by cluster.max_shards_per_node * number_of_data_nodes .
You may consider creating temporary breathing room for the cluster by removing unused indices or (less recommended) short-term overriding this setting.
Once your cluster has breathing room, kindly note it sounds like its oversharded and it may be time to scale out or use more rigorous ILM.