Steps to reproduce:
details here: https://unity.slack.com/archives/C027M1DPFJS/p1731592804033569

1. Use Play Mode scenario with a second player (goal: try to use Play Mode scenario in order to set a default starting scene and not use the active scene in the editor)
2.  click Play
3.  Notice the second editor is starting

Actual results: 

at the moment of the domain reload it looks like it is closing. Then the play mode starts on the main editor but a second window is not available.

Console warning and details are attached.

Play mode status is saying that instances are running properly.
With Default play mode, MPMM works properly and another instance starts as expected.

Expected results: 

No errors

Reproducible with versions: Unity 6.0.24f1, MPPM 1.3.1