Originally Posted by RingTailCat
I vaguely recall that there was a change to the party interface that reduced its functionality but increased its privacy or security or something like that. This might of been called a bug if your plugin had depended on it, i.e. the original behavior.
The issues with the party object had to do with the underlying C objects not always updating the Lua objects when party members joined or left causing the Lua Party object to eventually be out of synch with the actual party. There were some improvements made back in 2014 but I do not use the Party object (partly due to it being undependable) so you have limited ways to determine if all the bugs were properly addressed.
I'm not sure, but RingTailCat may be referring to the combat statistics that used to be available for your fellowship but are no longer supported (not directly related to the Party object issue). They were removed from the client for performance reasons. The Combat Analysis plugin in particular used to use those statistics and the code still exists since the author hoped the functionality would be restored but never was.
First, you could try to find the developer posts and see if any authors confirmed that the bugs were fixed (my cursory search turned up nothing so I don't know how easy that would be). Since the last round of significant Lua bug fixes was back in 2014, if you found posts about buggy behavior in 2016 it is not too likely it was completely fixed. Second, you could try to find a plugin author that is using the Party object in a currently supported plugin (which is why posting here was a good idea, but since there haven't been any definitive answers from other authors that may also not work well). Third, and most difficult, you can attempt to replicate the buggy behavior yourself. I believe that creating a Lua Party and repetitively adding/removing players with some overlap between the various additions/removals used to cause the Lua object to get out of synch after about twenty minutes of casual play (adding/removing players once a minute or so).
So, you can create a plugin that just displays a Lua based list of your party members and run with it for a while and see if it gets out of synch. The old workaround for this was to periodically reload the party-based plugin to get it's environment back in synch with the client.