Reproduction steps:
1. Open the attached “BugRepro” project
2. Open the “Assets/Scenes/SampleScene” Scene
3. In the ProBuilder window (Tools > ProBuilder > ProBuilder window), open the UV Editor window
4. In the Edit Mode toolbar, select Face mode
5. In the Scene view, select the “Arch” GameObject’s curve sidewall face
6. Autostitch the face above the selected sidewall face (hold CTRL and select the top face)
7. Observe the edge between the sidewall face from step 5 and autostitched face from step 6

Expected result: The textures at the edge align
Actual result: The textures are slightly off

Reproducible with: 5.0.3 (2021.3.23f1), 5.2.3 (2021.3.43f1, 2022.3.44f1), 6.0.3 (6000.0.17f1)

Reproducible on: Windows 11
Not reproducible on: No other environments tested