Here are the changes in 1.5.1 (hotfix):

  • Klowns
    • Fixed an issue where Fluxo, Gutso, Slappy and Impy were invulnerable to certain types of damage

  • Humans

    • Fixed an issue where fully Charged Attacks would revert to uncharged attacks after swinging

Patch 1.5.1 · Killer Klowns From Outer Space: The Game patch notes · SteamPeaks