First message from any slack user dropped.

[robsiemb]

On the first message the bot tries to forward from slack for a given user, it attemps to send them a DM to introduce itself and tell them what their bridged display name is.

However, it does this with a now-obsolete API, and so it gets an exception instead. This happens before the message is forwarded, so the message isn't forwarded. The slack error is:

'messages': ['[ERROR] This method is retired and can no longer be used. Please use conversations.open instead. Learn more: [https://api.slack.com/changelog/2020-01-deprecating-antecedents-to-the-conversations-api.']}}](https://api.slack.com/changelog/2020-01-deprecating-antecedents-to-the-conversations-api.']%7D%7D)\n"

Future messages are fine, since the user is now known to the bot.