Just to elaborate a bit, when any button is clicked there will be a state change. State is modeled with Provider pattern, so effectively a render will be called on all components that are dependent on state.
As initially panel renders correctly, the issue seems to be related to UI re-builds, specifically first rebuild after load.
When re-render works correctly, I can also notice that panel for a brief second is in that broken state, but restores to the right sizes after the blink.
@Erin_Finnegan You can find a very simple reproduction repo here: GitHub - AAverin/adobe-uxp-react-playground
It is based on react starter, with the addition of very simple reducer and state, changing UI based on what is inside. Clicking on any button after first load blinks with a broken state where flex stops working.
Removing react-styled-flexboxgrid from the dependencies seems to resolve the issue. Even though it is a quite basic styled wrapper for css to support grids
The engineering team still requested we test this and open a JIRA bug, because in your previous sample they “couldn’t see any unsupported CSS properties…”
@Erin_Finnegan This could be some localized issue of flexboxgrid package as it’s not really supported for the past 3 years. On the other hand, there isn’t much to support there, it is a pretty basic wrapper using styled-components.
Anything I can do to help besides providing the sample? I couldn’t reproduce a completely broken state in the sample, but at very least it blinks with flex not working or styles not working correctly. Hope that is enough.