I keep getting `unrefdHandle`

I added `block-trace` to my setup, and I'm frequently seeing:

```
Error: CPU is blocked
app_1 | at Timer.unrefdHandle (timers.js:453:22)
```

This makes it a little hard to debug. Do you have any ideas why I might be `unfredHandle` and how to improve the situation to expose the actual function/line that is erroring (as per the README.md)?

Start with README.md and reproduce the reported block-trace output ending at timers.js:453:22 in Timer.unrefdHandle. Trace how the setup produces this stack trace and determine whether the actual blocking function and line can be exposed instead. Done means the error identifies the relevant application function and line rather than only the timer handler.

Written by the indexing model from the issue text.