Run Sampler, select TableView2 sample, right click on a column header cell to fix it, this exception shows up:
Exception in thread "JavaFX Application Thread" java.lang.StackOverflowError
at javafx.base/javafx.collections.ListChangeBuilder.insertAdd(ListChangeBuilder.java:127)
at javafx.base/javafx.collections.ListChangeBuilder.nextAdd(ListChangeBuilder.java:254)
at javafx.base/javafx.collections.ObservableListBase.nextAdd(ObservableListBase.java:185)
at javafx.base/javafx.collections.ModifiableObservableListBase.add(ModifiableObservableListBase.java:160)
at java.base/java.util.AbstractList.add(AbstractList.java:111)
at javafx.controls/javafx.scene.control.CheckMenuItem$1.invalidated(CheckMenuItem.java:144)
at javafx.base/javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:110)
at javafx.base/javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:145)
at javafx.base/com.sun.javafx.binding.BidirectionalBinding$BidirectionalBooleanBinding.invalidated(BidirectionalBinding.java:256)
at javafx.base/com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(ExpressionHelper.java:136)
at javafx.base/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
at javafx.base/javafx.beans.property.BooleanPropertyBase.fireValueChangedEvent(BooleanPropertyBase.java:104)
at javafx.base/javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:111)
at javafx.base/javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:145)
at org.controlsfx.controls@11.2.3-SNAPSHOT/org.controlsfx.control.action.Action$2.set(Action.java:165)
at org.controlsfx.controls@11.2.3-SNAPSHOT/org.controlsfx.control.action.Action.setSelected(Action.java:194)
at org.controlsfx.controls@11.2.3-SNAPSHOT/org.controlsfx.control.tableview2.actions.ColumnFixAction.lambda$new$0(ColumnFixAction.java:117)
at javafx.base/com.sun.javafx.collections.ListListenerHelper$Generic.fireValueChangedEvent(ListListenerHelper.java:321)
at javafx.base/com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(ListListenerHelper.java:73)
at javafx.base/javafx.collections.ObservableListBase.fireChange(ObservableListBase.java:239)
at javafx.base/javafx.collections.ListChangeBuilder.commit(ListChangeBuilder.java:482)
at javafx.base/javafx.collections.ListChangeBuilder.endChange(ListChangeBuilder.java:541)
at javafx.base/javafx.collections.ObservableListBase.endChange(ObservableListBase.java:211)
at javafx.base/javafx.collections.ModifiableObservableListBase.add(ModifiableObservableListBase.java:162)
at java.base/java.util.AbstractList.add(AbstractList.java:111)
at org.controlsfx.controls@11.2.3-SNAPSHOT/org.controlsfx.control.tableview2.actions.ColumnFixAction.lambda$initialize$2(ColumnFixAction.java:149)
at org.controlsfx.controls@11.2.3-SNAPSHOT/org.controlsfx.control.action.Action.setSelected(Action.java:196)
at org.controlsfx.controls@11.2.3-SNAPSHOT/org.controlsfx.control.tableview2.actions.ColumnFixAction.lambda$new$0(ColumnFixAction.java:117)
at javafx.base/com.sun.javafx.collections.ListListenerHelper$Generic.fireValueChangedEvent(ListListenerHelper.java:321)
at javafx.base/com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(ListListenerHelper.java:73)
at javafx.base/javafx.collections.ObservableListBase.fireChange(ObservableListBase.java:239)
at javafx.base/javafx.collections.ListChangeBuilder.commit(ListChangeBuilder.java:482)
at javafx.base/javafx.collections.ListChangeBuilder.endChange(ListChangeBuilder.java:541)
at javafx.base/javafx.collections.ObservableListBase.endChange(ObservableListBase.java:211)
at javafx.base/javafx.collections.ModifiableObservableListBase.remove(ModifiableObservableListBase.java:190)
at javafx.base/javafx.collections.ModifiableObservableListBase.remove(ModifiableObservableListBase.java:178)
at org.controlsfx.controls@11.2.3-SNAPSHOT/org.controlsfx.control.tableview2.actions.ColumnFixAction.lambda$initialize$2(ColumnFixAction.java:151)
at org.controlsfx.controls@11.2.3-SNAPSHOT/org.controlsfx.control.action.Action.setSelected(Action.java:196)
...
Also note that the first column should be fixed but it is not:
getFixedColumns().setAll(fullNameColumn);

Run Sampler, select TableView2 sample, right click on a column header cell to fix it, this exception shows up:
Also note that the first column should be fixed but it is not: