Grav Admin 1.8.18 fails to upgrade

I tried several times to upgrade the Admin plugin from version 1.8.17 to 1.8.18 on my Windows machine. admin.php, admin.yaml and several other files (sometimes even ALL files!) are removed after the update and of course the admin panel is completely broken.
I never experienced that before.
For now I revert to 1.8.17… is someone else experiencing this issue?