No, it's not just you: Slack behaves strangely from Friday morning.
The list of issues is extensive: Some messages do not go through and others will not allow users to edit them. Links do not necessarily show an example, and some files that attempt to be uploaded will not be uploaded or two messages will appear twice.
In short, Slack functionality on Friday morning is irregular and incessant.
The company says that problems started just before. 8.00 ET Friday morning and has passed the following hour.
In our experience – Business Insider uses Slack as our main communication tool – the service is functional but unpredictable.
For example: Messages appear as "unable to send" and when "Retry" is clicked, the message is sent twice.
If you want to be as up to date as possible when Slack gets fixed, go over to the Slack status website here.