How to reproduce:
1. Add the attached project ("Reports.zip") to your preferred workspace
2. Open it and connect it to Perforce
3. Submit the "1" and "2" materials
4. Open P4V with a different user and lock the "1" material
5. Check out the "2" material and go to "Simple Window" -> "Submit" to submit both "1" and "2" materials
6. Observe the console and the material status

Expected result: the "2" material is submitted and the "1" material is not (Or alternatively another prompt is called letting the user choose whether to submit just the submittable assets or nothing at all)
Actual result: neither material gets submitted and a "Version Control: File(s) couldn't be locked." error is thrown

Reproduced in: 2020.1.0a3, 2019.3.0b2, 2019.2.3f1, 2018.4.8f1, 2017.4.32f1

Note: Reproduces when submitting multiple assets with the context menu or when using Provider.Submit