I also found that there was an issue where if the number of rows exceeded four, then they weren't updating correctly. I fixed this in the new version which you can get Here Animation Exporter 1.5 I apologize to anyone that may have experienced troubles.
Here's a list of features to the update.
V1.5 by Will Canada
Adjusted logic error that was causing frames to, under certain conditions, be drawn outside of the sprite sheet.
In the previous version the script placed the last layer as the first frame, this was counter-intuitive to photoshop, script
now places first layer as first frame.
Fixed Issue where the number of rows wasn't properly scaling beyond a certain threshold.
Corrected spelling error in a user prompt.