A while back I ran into an issue where the opening of an existing network file share was slow. After connecting to that specific share on an Android or iOS device it could take up to 30 seconds before the share would open. Sometimes it would remain in a loop ( android ) or show an connection time-out ( iOS ).
The problem was not in the size or number of files and folders but it was related to some hidden files in the share. After deleting these files the shares can be browsed normal speed!