How to reproduce:
1. Open the attached "Input Tester 2.zip" project
2. Open the "Input Tester" Scene -> Enter the Play Mode
3. Press the destined button (see in the edit) on any selected device (keyboard, mouse, xbox1 controller, PS4 controller )
4. Press a button on another device

Expected result: Both players are successfully created
Actual result: The input becomes broken (see the scenarios in the notes)

Reproducible with: 2018.4.29f1 (0.2.1-preview), 2019.4.13f1 (0.9.4-preview)2020.1.11f1 (1.0.0-preview.3), 2020.2.0b9 (1.0.0), 2021.1.0a3(1.1.0-preview.2)

Notes:
- Debug messages return values of 1 or 0 to tell which inputs are On or Off
- If you have only mouse and keyboard connected(which is the default) you are able to add new players after each created player as you should
- If you have 1 ps4 controller connected, spawning the first player with the mouse causes the start button to become broken
- If you have 2 ps4 controllers connected, spawning the first player with mouse or keyboard causes the start button to become broken
- All other device combinations I tested causes the start button to become broken immediately after spawning a player
- If you plugin or unplug a device while the game is running the start button becomes unbroken
- When all connected devices are bound to a player (not the input manager) the start button remains unusable, but the test buttons become usable by all devices.