Dropped frames issues occur as a result of degraded performance. Many factors can contribute to this, including file fragmentation. Xsan includes a file defragmentation utility that you can run from the command line. To defragment an Xsan volume, type this command in Terminal:
sudo /Library/Filesystems/Xsan/bin/snfsdefrag -rv <PathToDirectory>
...where <PathToDirectory> is the path to the directory where your media or render files are stored. Other factors that may contribute to dropped frame issues can be found in this article.
Note: It is also necessary to run snfsdefrag -dv after performing bandwidth expansion on an Xsan Volume.