First of all: Using and loving your plugin ever since it's release!
TypeError: i.querySelector(...) is null
It happens on the normal posts edit screen, which I activated following your instructions. On the pages edit screen, it works fine.
When I reload the page, the title is displayed correctly again.
I both cases, actual re-ordering works fine, both errors just make the plugin 'feel broken'.
Hopefully, the hints will be helpful for you.