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Customizable Object compilation out of date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
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Within your character’s CO, disconnect your group pin
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Compile
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Reconnect the pin
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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.