You are not using a fixed location for your labels therefore the partials strategy is unable to work correctly as it needs to know exactly where the label is going to be drawn on each tile.

Add the following at the top of your TextSymbolizer to force where the label should appear:

<Geometry>
  <ogc:Function name="centroid">
    <ogc:PropertyName>the_geom</ogc:PropertyName>
  </ogc:Function>
</Geometry>

You are not using a fixed location for your labels therefore the partials strategy is unable to work correctly as it needs to know exactly where the label is going to be drawn on each tile.

Add the following at the top of your TextSymbolizer to force where the label should appear:

<Geometry>
  <ogc:Function name="centroid">
    <ogc:PropertyName>the_geom</ogc:PropertyName>
  </ogc:Function>
</Geometry>

This, of course, assumes your geometry attribute is called the_geom change it if necessary to match your features. Also make sure that you have turned off your browser caching while you are testing this. I would also remove the following as there is no telling what the interactions between all of those options is:

        <VendorOption name="spaceAround">-1</VendorOption>
        <VendorOption name="group">yes</VendorOption>
        <VendorOption name="labelAllGroup">true</VendorOption>
        <VendorOption name="conflictResolution">false</VendorOption>