Filters move to bottom in admin grid

You need to define dependency in your module.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Namespace_Modulename" setup_version="1.0.0">
        <sequence>
            <module name="Magento_Sales" />
        </sequence>
    </module>
</config>

disable and re enable your module and check.

Please define dependencies in your module so that your module will load after the dependent one.

Add this code into your module.xml file

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Vendor_Modulename" setup_version="2.0.0"/>
    <sequence>
        <module name="Magento_Sales" />
    </sequence>
</config>

Please refresh the cache after this.