diff --git a/src/container/srv_container.c b/src/container/srv_container.c
index bf9ebdeddaa..9f194969fa8 100644
--- a/src/container/srv_container.c
+++ b/src/container/srv_container.c
@@ -1712,10 +1712,12 @@ cont_ec_agg_alloc(struct cont_svc *cont_svc, uuid_t cont_uuid,
 	ec_agg->ea_servers_num = rank_nr;
 	ec_agg->ea_current_eph = 0;
 	ec_agg->ea_rdb_eph     = 0;
+	ec_agg->ea_start_ts     = daos_gettime_coarse();
+	ec_agg->ea_warn_slug_ts = ec_agg->ea_start_ts;
 	for (i = 0; i < rank_nr; i++) {
 		ec_agg->ea_server_ephs[i].rank = doms[i].do_comp.co_rank;
 		ec_agg->ea_server_ephs[i].eph = 0;
-		ec_agg->ea_server_ephs[i].ee_update_ts = daos_gettime_coarse();
+		ec_agg->ea_server_ephs[i].ee_update_ts = ec_agg->ea_start_ts;
 	}
 	d_list_add(&ec_agg->ea_list, &cont_svc->cs_ec_agg_list);
 	*ec_aggp = ec_agg;
@@ -1776,6 +1778,22 @@ ds_cont_leader_update_agg_eph(uuid_t pool_uuid, uuid_t cont_uuid,
 			if (ec_agg->ea_server_ephs[i].eph < eph) {
 				ec_agg->ea_server_ephs[i].eph = eph;
 				ec_agg->ea_server_ephs[i].ee_update_ts = daos_gettime_coarse();
+			} else if (eph == 0 && ec_agg->ea_current_eph != 0) {
+				/*
+				 * A rank reports zero only while its EC aggregation is paused
+				 * waiting for the boundary (sc_ec_agg_eph_valid == 0), e.g. a
+				 * reintegrated/extended rank that got the VOS container after the
+				 * last refresh. Ask cont_agg_eph_sync() to re-send the current
+				 * boundary even if the minimum epoch did not change, otherwise
+				 * the rank never starts and pins the boundary forever.
+				 * (ea_current_eph == 0 refreshes every round anyway.)
+				 */
+				if (!ec_agg->ea_need_refresh)
+					D_INFO(DF_CONT ": rank %u waits for EC agg boundary, "
+						       "current " DF_X64 "\n",
+					       DP_CONT(pool_uuid, cont_uuid), rank,
+					       ec_agg->ea_current_eph);
+				ec_agg->ea_need_refresh = 1;
 			}
 			break;
 		}
@@ -1850,9 +1868,9 @@ ds_cont_tgt_refresh_agg_eph(uuid_t pool_uuid, uuid_t cont_uuid,
 	uuid_copy(arg.cont_uuid, cont_uuid);
 	arg.min_eph = eph;
 
-	rc = ds_pool_task_collective(pool_uuid, PO_COMP_ST_NEW | PO_COMP_ST_DOWN |
-				     PO_COMP_ST_DOWNOUT, cont_refresh_vos_agg_eph_one,
-				     &arg, DSS_ULT_FL_PERIODIC);
+	rc = ds_pool_task_collective(pool_uuid,
+				     PO_COMP_ST_NEW | PO_COMP_ST_DOWN | PO_COMP_ST_DOWNOUT,
+				     cont_refresh_vos_agg_eph_one, &arg, DSS_ULT_FL_PERIODIC);
 	if (rc) {
 		DL_ERROR(rc, DF_CONT ": refresh ec_agg_eph " DF_X64 " failed.",
 			 DP_CONT(pool_uuid, cont_uuid), eph);
@@ -2074,7 +2092,14 @@ cont_agg_eph_sync(struct ds_pool *pool, struct cont_svc *svc)
 		if (min_eph < ec_agg->ea_rdb_eph)
 			min_eph = ec_agg->ea_rdb_eph;
 
-		if (min_eph == ec_agg->ea_current_eph && ec_agg->ea_current_eph != 0)
+		/*
+		 * Skip the refresh when nothing changed, unless some rank asked for the
+		 * boundary (see ds_cont_leader_update_agg_eph()). Such a rank has eph 0,
+		 * so min_eph is pinned to ea_rdb_eph == ea_current_eph and it would never
+		 * get the boundary it needs to start reporting.
+		 */
+		if (min_eph == ec_agg->ea_current_eph && ec_agg->ea_current_eph != 0 &&
+		    !ec_agg->ea_need_refresh)
 			continue;
 
 		/**
@@ -2094,6 +2119,7 @@ cont_agg_eph_sync(struct ds_pool *pool, struct cont_svc *svc)
 			ec_agg->ea_warn_slug_ts = cur_ts;
 
 		} else if (cur_eph && new_eph > cur_eph && (new_eph - cur_eph) >= 600 &&
+			   (cur_ts - ec_agg->ea_start_ts) >= (new_eph - cur_eph) &&
 			   (cur_ts - ec_agg->ea_warn_slug_ts) >= 600) {
 			ec_agg->ea_warn_slug_ts = cur_ts;
 			D_WARN(DF_CONT ": Sluggish EC boundary reporting. "
@@ -2120,6 +2146,10 @@ cont_agg_eph_sync(struct ds_pool *pool, struct cont_svc *svc)
 			}
 		}
 
+		/* clear before the refresh (which yields), so a request arriving meanwhile
+		 * triggers another refresh in the next round.
+		 */
+		ec_agg->ea_need_refresh = 0;
 		rc = cont_iv_ec_agg_eph_refresh(pool->sp_iv_ns, ec_agg->ea_cont_uuid, min_eph,
 						svc->cs_ec_leader_ephs_req);
 		if (rc) {
diff --git a/src/container/srv_internal.h b/src/container/srv_internal.h
index d53205a4be1..bd27d232c0a 100644
--- a/src/container/srv_internal.h
+++ b/src/container/srv_internal.h
@@ -69,11 +69,20 @@ struct cont_ec_agg {
 	uuid_t			ea_cont_uuid;
 	daos_epoch_t		ea_current_eph;
 	daos_epoch_t             ea_rdb_eph;
+	/* time when this leader started tracking the container. A boundary jump larger
+	 * than the tracking age cannot have been observed by this leader, it comes from
+	 * the stale epoch loaded from rdb at leader step-up, so it is not a real stall.
+	 */
+	uint64_t                 ea_start_ts;
 	uint64_t                 ea_warn_slug_ts;
 	struct ec_eph		*ea_server_ephs;
 	d_list_t		ea_list;
 	int			ea_servers_num;
-	uint32_t                 ea_deleted : 1;
+	uint32_t                 ea_deleted : 1,
+	    /* some rank reported eph 0 (its EC aggregation waits for the boundary), re-send the
+	     * boundary in the next cont_agg_eph_sync() even if the minimum epoch did not change.
+	     */
+	    ea_need_refresh                 : 1;
 };
 
 /*