Have you ensured that you have set the second character to Auto Receive Input from Player0? You can do this by going to your character blueprint, going to the Viewport and in the Details panel, going to the Input section. You should then see Auto Receive Input and can verify whether or not it is set to Player0. This could potentially be causing an issue.
If you have already done this and verify that it is correct, could you perhaps zip up and attach your project so that I could look into the issue a bit further and see how you have things set up? If you zip up the file and it is too large to attach, you can upload it to Dropbox or Google Drive and provide me with a link. If you are uncomfortable attaching the file publicly, feel free to send me a private message with the link to your project so that I can take a closer look.
I’ve deleted and created again the project before seeing your answer, sorry.
I’ve recreated my basics blueprints and I think the error was coming from the option “Auto Receive Input” that I don’t modified on the last project but I place to “Player 0” by default this time.