Solving the replica issue now allowed me to get better insights into why the one index is red.
{ "index" : "events-training_stats_scalar-d1bd92a3b039400cbafc60a7a5b1e52b", "shard" : 0, "primary" : true, "current_state" : "unassigned", "unassigned_info" : { "reason" : "CLUSTER_RECOVERED", "at" : "2021-11-09T22:30:47.018Z", "last_allocation_status" : "no_valid_shard_copy" }, "can_allocate" : "no_valid_shard_copy", "allocate_explanation" : "cannot allocate because all found copies of the shard are either stale or corrupt", "node_allocation_decisions" : [ { "node_id" : "CldaHbiyQWaNcpWtVab35w", "node_name" : "clearml", "transport_address" : "172.28.0.5:9300", "node_attributes" : { "ml.machine_memory" : "34244124672", "xpack.installed" : "true", "ml.max_open_jobs" : "20" }, "node_decision" : "no", "store" : { "in_sync" : true, "allocation_id" : "emdrRuHVQ8asg5LU_HVkGw", "store_exception" : { "type" : "corrupt_index_exception", "reason" : "failed engine (reason: [refresh failed source[refresh_flag_index]]) (resource=preexisting_corruption)", "caused_by" : { "type" : "i_o_exception", "reason" : "failed engine (reason: [refresh failed source[refresh_flag_index]])", "caused_by" : { "type" : "corrupt_index_exception", "reason" : "codec footer mismatch (file truncated?): actual footer=0 vs expected footer=-1071082520 (resource=BufferedChecksumIndexInput(NIOFSIndexInput(path=\"/usr/share/elasticsearch/data/nodes/0/indices/T5e15fRWTvW69oI3Cm2BeQ/0/index/_e1il.fdt\")))" } } } } } ] }