iOS: Slider sometimes does not mount at full width

[marcshilling]

Environment

• react-native info output:

// react-native info
npmPackages:
  "@react-native-community/cli":
    installed: 15.1.3
    wanted: ^15.0.1
  react:
    installed: 18.3.1
    wanted: 18.3.1
  react-native:
    installed: 0.77.3
    wanted: ^0.77.0
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true

Description

On initial mount of a new component that contains a slider, the slider will very rarely not expand to full width even though we have styled it as such. Here's a screenshot:

In this example the slider is being set with an initial value of 3.6 (out of 5.0), but you can see the actual track of the slider is only rendering at less than half the width that it should be. Note that we render the tick-marks ourselves, not via the repo, but they show that we expect the slider to be full width. The slider still functions normally at this point, allowing selection of values 0 to 5 but only along this tiny track. 98% of the time when pushing this screen it appears normally...this just appears to be an odd race condition.

This only started happening after I upgraded from RN 0.76 to 0.77 and enabled the new architecture, and upgraded slider from 4.5.0 to 5.0.1. I suspect it's related to new arch.

Reproducible Demo

Not reproducible every time so this is tough. But it's a slider with style={{ width: '100%' }} set and the component is presented via a react-native-navigation (wix) modal