>Standups are in my experience much more effective at signalling blocking issues than slack.

Your messaging tool is not good enough to communicate urgency? You cannot send a message and say "this is urgent" and have somebody read it and respond in a timely manner? You would have better luck waiting until the next standup meeting?

>Nobody is going to spend their day checking what other people are doing on Jira

Your primary work tracking tool is not good enough to allow people to see who is working on what, and what the status of that work is? You can't get an overview of what is being worked on? You can't check on a specific issue to see how far along it is?

Here's how it works when you use your tools:

1. You have an urgent issue. You message the involved parties. Your message should communicate the urgency of the issue. They read it and respond / take action within an appropriate amount of time.

2. You want to know what your team is working on. You look at your issue tracker to see what everyone is working on. If you are curious about the status of any work in particular, you look at the details for that work. If there is insufficient information about its progress, you send the assignee a message (see #1).