Some dividers are randomly missing

For some reason, the white dividers between rows are randomly not appearing sometimes:

My code to render the heatmap looks like

```
({
background: `rgb(40, 167, 59, ${1 - (max - value) / (max)})`,
})}
title={(value, unit) => `${value}/${actors.size}`}
/>
```
Any idea what could be causing this?

Start by reproducing the missing dividers with the provided HeatMap props and inspect the component's row and cell rendering behavior. Confirm the conditions that make the white dividers disappear, then verify that the dividers render consistently across the affected rows.

Written by the indexing model from the issue text.