Reliable `chat_member` Leave Updates Are Missing in Large Telegram Groups

[Spideyofficial777]

Reliable chat_member / Leave Updates in Large Groups

Summary

Bots do not always receive reliable chat_member updates when users leave very large groups. This makes it impossible to maintain accurate member state or send goodbye messages consistently.

Environment

• Telegram Bot API: Latest
• Update Type: chat_member
• Bot is administrator: Yes
• allowed_updates includes "chat_member"
• Single bot instance: Yes

Problem

In large groups, some leave events are never delivered to the bot.

When this happens:

• No chat_member update is received.
• No left_chat_member service message exists.
• The bot cannot determine which user left.
• Goodbye messages are skipped.
• Internal member state becomes inconsistent.

This affects moderation bots that rely on accurate member lifecycle events.

Expected Behavior

Every member leave should generate a reliable chat_member update for administrator bots.

If guaranteed delivery is not possible, an official reconciliation mechanism would be extremely helpful.

Examples:

• Incremental member change API
• Missed event recovery endpoint
• Reliable member event cursor
• Official member synchronization API

Impact

Large moderation bots cannot guarantee:

• Goodbye messages
• Accurate member tracking
• Reliable moderation logs
• Consistent automation

Developers are forced to implement complex workarounds that still cannot achieve 100% accuracy because the missing event is never exposed through the Bot API.

Request

Please consider improving the reliability of member updates for large groups or providing an official reconciliation mechanism for missed membership events.

Thank you for your work on the Telegram Bot API.

[levlam]

chat_member updates are received in all chats regardless of their size.