Reproduction steps:
1. Create a new project (“3D Core” template is enough)
2. Open Window > Analysis > Profiler
3. Record a few seconds of either “Edit Mode” or “Play Mode” by pressing the Record button
4. Under Timeline, resize the “Main Thread” and “Render Thread”
5. Observe them being resizable
6. Try resizing “Job”, “Loading” or other threads

Expected result: Hovering over the separation line between other threads shows a resize icon and the threads can be resized
Actual result: Hovering over the separation line between other threads shows a resize icon, however, when trying to resize it, the “Render Thread” is resized instead

Reproducible with: 2021.3.52f1, 2022.3.63f1, 6000.0.50f1, 6000.1.6f1, 6000.2.0b4

Reproduced on: Windows 11 Pro (24H2), macOS 15.4.1 Arm64
Note reproduced on: No other environment tested

Notes:
- Reproducible in a new project
- It should either not show the resize icon on the cursor when hovering over the separation line of an unresizable thread, or allow resizing all of the threads on the Timeline
- It is possible to resize individual threads but not the group threads