The S905 also has this same issue.  There is micro-stuttering when subtitles are displayed.  I disable subtitles and it plays perfectly.  It doesn't always stutter in the same spot when I replay a scene that initially had a stutter.  Some scenes are more prone to stuttering than others.
	 
	
	
I noticed that too with my 905x, but not only the first Subtitle. It appeare randomly , ca. every 20th Sub, both types, SRT in MKV or SUP embedded in m2ts/Blu-ray Structur.