Entering -d3d12 in the game’s launch options field can help resolve the issue.
Steps:
1) Open Steam.
2) Right-click METAL SLUG ATTACK RELOADED in your Steam library, then click Properties.
3) Enter the value -d3d12 in the General > LAUNCH OPTIONS field.
4) Launch the game.
If the issue occurs pre-battle during the tutorial, please give the above a try.