Progress events internally have a completed count and a total count, which can mean that for a job with 20000 total counts, then there will be 20000 events fired. Sending all these events to the IDE can break it. For example, debugging a huge binary resulted in around 50 million messages, which rendered the IDE useless, as it was spending all of its resources simply parsing messages and updating the UI.
A way to fix this is to send unique percentage updates, which are at most 100 per job, which is not much. I was able to debug that big target and confirm that only unique percentage notifications are sent. I can't write a test for this because the current test is flaky. I'll figure out later how to make the test reliable, but fixing this will unblock us from deploy a new version of lldb-vscode.
These are the unique progress events in the logs
The progress UI in VSCode looks like this