Hello, I am not sure if I am the first one to find this bug, but...
How to reproduce:
Create field FieldsetTabOpen (lets name test_tab)
Create field Page (lets name test), choose Multiple pages, and type PageListSelectMultiple
Add the fields to template:
test_tab
test
test_tab_END
The field "test" is not sortable. The reason is because the InputfieldPageListSelectMultiple.init is called before the tabs are rendered.
My very quick workaround was to move the init method call into setTimeout, but I am not sure if this the correct choice.
wire/modules/Inputfield/InputfieldPageListSelect/InputfieldPageListSelectMultiple.module:88 now looks like the line below.
"setTimeout(function() { InputfieldPageListSelectMultiple.init($('#{$this->id}_items')); }, 200);" .