Normal behavior:

1. Setup Slack webhook with "alarm" type (https://www.zabbix.com/ru/integrations/slack)
2. Add contact with Slack channel #channel (private)
3. Receive ALARM message to #channel
4. Receive UPDATE under message thread
5. Receive RECOVERY by changing the original message title and color

But if we want to use 2 or more Slack channels/contact the behavior is incorrect:

• UPDATE messages locate just in Slack channel, not under the message thread
• RECOVERY events are sent (Zabbix logs are ok), but they don't reach Slack channels

Steps to reproduce:

1. Setup Slack webhook with "alarm" type (https://www.zabbix.com/ru/integrations/slack)
2. Add contact1 with Slack channel #channel1 (private)
3. Add contact2 with Slack channel #channel2 (private)
4. Simulate the problem
5. We receive ALARM message in both Slack channels (#channel1 and #channel2)

1. Simulate the recovery or update message
2. No RECOVERY message

Result:

1. ALARM message (same in #channel1 and #channel2)

2. UPDATE message (same in #channel1 and #channel2)

3. No RECOVERY message received in Slack channels!

4. Under tags section in problem list we see

2 channel ids, 2 channel names, 2 message links and 2 message timestamps.

Disabling all other Slack contacts except 1 solves the problem.

Expected:
We expect that sending notifications in 2 or more Slack channels should work like in case of 1 Slack channel.