I will copy the description from the original issue Dart-Code/Dart-Code#4555 (comment)

Describe the bug
During debug, hovering a value doesn't show its value anymore.

To Reproduce
Steps to reproduce the behavior:

1. Run some code
2. Break in a breakpoint then hover some variable
3. Most of the times it happens inside of a builder

Expected behavior
To show the value of the variable.

Please complete the following information:

Operating System and version: MacOS 13.5.2
VS Code version: 1.82.2
Flutter 3.13.4 • channel stable •
https://github.com/flutter/flutter.git
Framework • revision 367f9ea16b (2 weeks ago) •
2023-09-12 23:27:53 -0500
Engine • revision 9064459a8b
Tools • Dart 3.1.2 • DevTools 2.25.0

It appeared in Dart 3.0.1, Flutter 3.10.1