diff --git a/backend/internal/builder/builder.go b/backend/internal/builder/builder.go
index dd7bb675a..f7c0d2f91 100644
--- a/backend/internal/builder/builder.go
+++ b/backend/internal/builder/builder.go
@@ -1,6 +1,7 @@
 package builder
 
 import (
+	"log"
 	"time"
 
 	"openreplay/backend/internal/handlers"
@@ -8,6 +9,7 @@ import (
 )
 
 type builder struct {
+	sessionID      uint64
 	readyMsgs      []Message
 	timestamp      uint64
 	lastMessageID  uint64
@@ -16,8 +18,9 @@ type builder struct {
 	ended          bool
 }
 
-func NewBuilder(handlers ...handlers.MessageProcessor) *builder {
+func NewBuilder(sessionID uint64, handlers ...handlers.MessageProcessor) *builder {
 	return &builder{
+		sessionID:  sessionID,
 		processors: handlers,
 	}
 }
@@ -41,18 +44,16 @@ func (b *builder) checkSessionEnd(message Message) {
 func (b *builder) handleMessage(message Message, messageID uint64) {
 	if messageID < b.lastMessageID {
 		// May happen in case of duplicated messages in kafka (if  `idempotence: false`)
+		log.Printf("skip message with wrong msgID, sessID: %d, msgID: %d, lastID: %d", b.sessionID, messageID, b.lastMessageID)
 		return
 	}
 	timestamp := GetTimestamp(message)
 	if timestamp == 0 {
-		//  May happen in case of messages that are single-in-batch,
-		// 		e.g. SessionStart or RawErrorEvent (emitted by `integrations`).
-
-		// TODO: make timestamp system transparent;
+		log.Printf("skip message with empty timestamp, sessID: %d, msgID: %d, msgType: %d", b.sessionID, messageID, message.TypeID())
 		return
 	}
 	if timestamp < b.timestamp {
-		// Shouldn't happen after messageID check  which is done above. TODO: log this case.
+		log.Printf("skip message with wrong timestamp, sessID: %d, msgID: %d, type: %d", b.sessionID, messageID, message.TypeID())
 		return
 	}
 
diff --git a/backend/internal/builder/builderMap.go b/backend/internal/builder/builderMap.go
index af2ecf0d5..d905cdb45 100644
--- a/backend/internal/builder/builderMap.go
+++ b/backend/internal/builder/builderMap.go
@@ -24,7 +24,7 @@ func NewBuilderMap(handlersFabric func() []handlers.MessageProcessor) *builderMa
 func (m *builderMap) GetBuilder(sessionID uint64) *builder {
 	b := m.sessions[sessionID]
 	if b == nil {
-		b = NewBuilder(m.handlersFabric()...) // Should create new instances
+		b = NewBuilder(sessionID, m.handlersFabric()...) // Should create new instances
 		m.sessions[sessionID] = b
 	}
 	return b