Steam pushed an update for improved mutations and now the mod loader doesn't want it to work. Here's the error it gave me. Hope it helps
=== Improved Mutations Errors ===
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs(43,36): error CS0246: The type or namespace name 'PreferDefaultBehaviorEvent' could not be found (are you missing a using directive or an assembly reference?)
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs(43,24): error CS0115: 'BurrowingClaws.HandleEvent(PreferDefaultBehaviorEvent)': no suitable method found to override
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs(27,142): error CS0103: The name 'PreferDefaultBehaviorEvent' does not exist in the current context
== Warnings ==
<...>\steamapps\workshop\content\333640\1207623704\Carapace.cs'.
<...>\steamapps\workshop\content\333640\1207623704\Carapace.cs'.
<...>\steamapps\workshop\content\333640\1207623704\Wings.cs'.
<...>\steamapps\workshop\content\333640\1207623704\Wings.cs'.
<...>\steamapps\workshop\content\333640\1207623704\Horns.cs'.
<...>\steamapps\workshop\content\333640\1207623704\Horns.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.
<...>\steamapps\workshop\content\333640\1207623704\BurrowingClaws.cs'.