Interactions over or inside iframes are not recorded (browsers do not propagate events from iframes to the parent document)
The script is not properly tested on websites with very high traffic. Because userTrack is self-hosted the maximum number of recordings stored depends on your server configuration, usually it is a good idea to limit the recordings to only store latest 1000-2000 recordings.
Recorded pages content, versions or updates are not stored. This happens because userTrack only stores the URL of the recorded pages, this means that the page content is only loaded when the record is being played and it is always the latest/current version of the page at that URL.
As a consequences of the previous point: if a user has to log-in in order to access a specific area of the website you will not be able to view recordings on that area as long as you are not logged in as well. Also, if you are logged in as a different user you may see their actions done on your user panel.
Currently userTrack does not work well with web components and the shadow-DOM or frameworks that use those technologies (like Polymer). This happens because encapsulated elements do not correctly respond to external artificially triggered events (eg: click).