diff --git a/src/libs/zbxcachehistory/cachehistory.c b/src/libs/zbxcachehistory/cachehistory.c
index c265096db09..19da3feccfe 100644
--- a/src/libs/zbxcachehistory/cachehistory.c
+++ b/src/libs/zbxcachehistory/cachehistory.c
@@ -3378,6 +3378,7 @@ int	zbx_hc_is_itemid_in(zbx_uint64_t itemid)
 
 	UNLOCK_CACHE;
 
+zabbix_log(LOG_LEVEL_CRIT, "%s(): %s", __func__, (SUCCCEED == res)? "item found in history cache" : "item NOT found in history cache");
 	return res;
 }
 
diff --git a/src/libs/zbxcachevalue/valuecache.c b/src/libs/zbxcachevalue/valuecache.c
index 2bbc6e0d62d..26d15a2f4cc 100644
--- a/src/libs/zbxcachevalue/valuecache.c
+++ b/src/libs/zbxcachevalue/valuecache.c
@@ -2522,9 +2522,13 @@ int	zbx_vc_add_values(zbx_vector_dc_history_ptr_t *history, int *ret_flush, int
 	int			i;
 	zbx_dc_history_t	*h;
 
+zabbix_log(LOG_LEVEL_CRIT, "In zbx_vc_add_values()");
 	if (SUCCEED != zbx_history_add_values(history, ret_flush, config_history_storage_pipelines))
 		return FAIL;
 
+zabbix_log(LOG_LEVEL_CRIT, "sleeping 10 sec after zbx_history_add_values(), before inserting data into value cache");
+zbx_sleep(10);
+
 	if (ZBX_VC_DISABLED == vc_state)
 		return SUCCEED;
 
@@ -2579,7 +2583,7 @@ int	zbx_vc_add_values(zbx_vector_dc_history_ptr_t *history, int *ret_flush, int
 	}
 
 	UNLOCK_CACHE;
-
+zabbix_log(LOG_LEVEL_CRIT, "End zbx_vc_add_values()");
 	return SUCCEED;
 }
 
@@ -2612,7 +2616,7 @@ int	zbx_vc_get_values(zbx_uint64_t itemid, unsigned char value_type, zbx_vector_
 	zbx_vc_item_t	*item, new_item;
 	int 		ret = FAIL, cache_used = 1;
 
-	zabbix_log(LOG_LEVEL_DEBUG, "In %s() itemid:" ZBX_FS_UI64 " value_type:%d count:%d period:%d end_timestamp"
+	zabbix_log(LOG_LEVEL_CRIT, "In %s() itemid:" ZBX_FS_UI64 " value_type:%d count:%d period:%d end_timestamp"
 			" '%s'", __func__, itemid, value_type, count, seconds, zbx_timespec_str(ts));
 
 	if (ITEM_VALUE_TYPE_BIN == value_type)
@@ -2658,7 +2662,7 @@ out:
 
 	UNLOCK_CACHE;
 
-	zabbix_log(LOG_LEVEL_DEBUG, "End of %s():%s count:%d cached:%d",
+	zabbix_log(LOG_LEVEL_CRIT, "End of %s():%s count:%d cached:%d",
 			__func__, zbx_result_string(ret), values->values_num, cache_used);
 
 	return ret;
diff --git a/src/libs/zbxexpression/evalfunc.c b/src/libs/zbxexpression/evalfunc.c
index 860738eddf8..1d6476570db 100644
--- a/src/libs/zbxexpression/evalfunc.c
+++ b/src/libs/zbxexpression/evalfunc.c
@@ -1656,7 +1656,7 @@ static int	evaluate_NODATA(zbx_variant_t *value, const zbx_dc_evaluate_item_t *i
 	char				*arg2 = NULL;
 	zbx_proxy_suppress_t		nodata_win;
 
-	zabbix_log(LOG_LEVEL_DEBUG, "In %s()", __func__);
+	zabbix_log(LOG_LEVEL_CRIT, "In %s()", __func__);
 
 	zbx_history_record_vector_create(&values);
 
@@ -1702,6 +1702,7 @@ static int	evaluate_NODATA(zbx_variant_t *value, const zbx_dc_evaluate_item_t *i
 			1 == values.values_num)
 	{
 		zbx_variant_set_dbl(value, 0);
+zabbix_log(LOG_LEVEL_CRIT, "evaluate_NODATA(): setting to 0, NODATA trigger will not fire");
 	}
 	else
 	{
@@ -1724,10 +1725,12 @@ static int	evaluate_NODATA(zbx_variant_t *value, const zbx_dc_evaluate_item_t *i
 				SUCCEED == zbx_hc_is_itemid_in(item->itemid)))
 		{
 			*error = zbx_strdup(*error, "historical data transfer from proxy is still in progress");
+zabbix_log(LOG_LEVEL_CRIT, "evaluate_NODATA(): historical data transfer from proxy is still in progress");
 			goto out;
 		}
 
 		zbx_variant_set_dbl(value, 1);
+zabbix_log(LOG_LEVEL_CRIT, "evaluate_NODATA(): setting to 1. YES, NODATA trigger WILL FIRE");
 
 		if (0 != item->proxyid && 0 != lazy)
 		{
diff --git a/src/libs/zbxtrapper/trapper.c b/src/libs/zbxtrapper/trapper.c
index e3f37f8f03f..693b7280462 100644
--- a/src/libs/zbxtrapper/trapper.c
+++ b/src/libs/zbxtrapper/trapper.c
@@ -1149,7 +1149,7 @@ static int	process_trap(zbx_socket_t *sock, char *s, ssize_t bytes_received, zbx
 
 	zbx_rtrim(s, " \r\n");
 
-	zabbix_log(LOG_LEVEL_DEBUG, "trapper got '%s'", s);
+	zabbix_log(LOG_LEVEL_CRIT, "trapper got '%s'", s);
 
 	if ('{' == *s)	/* JSON protocol */
 	{
diff --git a/src/zabbix_server/cachehistory/cachehistory_server.c b/src/zabbix_server/cachehistory/cachehistory_server.c
index 8f00de8ab2e..5d98faf400f 100644
--- a/src/zabbix_server/cachehistory/cachehistory_server.c
+++ b/src/zabbix_server/cachehistory/cachehistory_server.c
@@ -830,6 +830,7 @@ static int	add_history(zbx_dc_history_t *history, int history_num, zbx_vector_dc
 		zbx_vector_dc_history_ptr_append(history_values, h);
 	}
 
+zabbix_log(LOG_LEVEL_CRIT, "add_history(): history_num:%d history_values->values_num:%d", history_num, (int)(history_values->values_num));
 	if (0 != history_values->values_num)
 		ret = zbx_vc_add_values(history_values, ret_flush, config_history_storage_pipelines);