geoserver - Labels disappear while zooming

We are using GeoServer 2.10.0. While displaying the labels in the maps, the labels which are there on the border of the tiles(4*4) are not getting displayed properly. the labels can be seen after further zooming in or out(when they fall in the center of the tile and not in the border). in this image you can see the labels are being cut

On zooming further, the labels come properly, as expected

In the first image, the labels are cut.

But in the second image, we see on zooming further, the labels are shown as expected.

Please see the SLD.

SLD:

                       xsi:schemaLocation="http://www.opengis.net/sld StyledLayerDescriptor.xsd" 
                       xmlns="http://www.opengis.net/sld" 
                       xmlns:ogc="http://www.opengis.net/ogc" 
                       xmlns:xlink="http://www.w3.org/1999/xlink" 

                       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  
    pxs_gna_mobile_site
    
      Geo_Style_pxs_gna_mobile_site
      
        
          Geo_Rule_pxs_gna_mobile_site
          350000.0
          

            
              
                
                image/png
              
              40
            
          

          

                   
  
    geom
  

            
              candidate_code
            
            
              Arial

              12
              normal
              bold
            
            
              
                
                  0.5
                  0.5
                

                
                  5
                  5
                
              
            
            
                2
                
                    #FFFFFF

                
                     
            
              #000000
            
             -1
            true
            yes
            true
            false

          
        
        
        Geo_Rule_pxs_gna_mobile_site
          350000.0
          
            
              
                
                image/png

              
              40