Mutable Plugin mesh does not update in PIE

The warning at the top of the screen
Customizable Object compilation out of date
is warning you about exactly this. Mutable is a little buggy but it works fine if you

  1. Within your character’s CO, disconnect your group pin

  2. Compile

  3. Reconnect the pin

  4. Compile again
    I know that’s ridiculous but after working with mutable for many long hours some things don’t update unless you disconnect the pin, recompile, and reconnect the pin again. I imagine it’ll be fixed in the next release, it is brand new after all.