I will preface this by saying I use an old version of REAPER - 4.22 - however, this has never happened before until now.
I applied an effect with ReaVerb on several channels, but when I rendered the file to MP3, the effect seemed to be noticeably delayed.
Audio directly from REAPER:
http://vocaroo.com/i/s0ef39TzuoZl
(achieved through recording Stereo Mix in Audacity)
Audio as a rendered MP3:
http://vocaroo.com/i/s104FplCGDFW
No changes in plugin settings have been applied between recording Stereo Mix in Audacity and rendering as MP3 in REAPER.
There are other effects that have been applied overall (ReaComp on the Master channel, which is something I do anyway), but since this doesn't cause an issue inside REAPER, why is it affecting the recording when it is being rendered? It's not a case of the generated reverb being compressed because again, this has never happened before: I've always had this setup and it has never been a problem (I've used ReaVerb alongside ReaComp in other projects to no complaint).
Any ideas as to what's happening here and how to solve it? The only solution I've got when it comes to rendering is just have Audacity open in another window, record the Stereo Mix and play the track in REAPER.
-edit-
I should also note that this is only a recent problem: I have rendered the audio in this project as MP3 in the past with no "late reverb" - no changes in plugin settings were made that could affect the render in anyway, at least not to my knowledge.