Rendering issue in devtools scope tree

## Problem
We have recently noticed the following rendering issue with the devtools scope tree.


## Environment / Observations

- this started happening a few weeks back.
- seems to happen intermittently although presently it is all the time.
- happens both on my Linux Ubuntu (Ubuntu 18.04.3 LTS) desktop and a colleague's Windows 10.
- Chrome Version 77.0.3865.75 (Official Build) (64-bit)
- Chrome restart does not clear it.
- Playing with docking position does not change anything.
- Sometimes I have seen it render some of the vars but not all of them if you resize the devtools scope panel.
- If you disable custom formatters in settings, it renders fine but alas back to raw JS data structures.
- Rendering same ds in console via `js/console.log` does the right thing and expandable tree renders perfectly.

This might be a cljs-devtools issue I see latest 0.9.10 was released over a year ago. I'm not sure but did dirac embed the devtools and is it possibly running a more up to date version ? (we don't use dirac at the moment, but if installing it instead of cljs-devtools would that solve it ?