EDIT:
maybe it is all over the manual ... but just in case:
it seems that indeed you need to empty the files from your replay folder, when doing a new event, or create and choose a new (empty) folder or subfolder.
I found no other way to get IRP to start afresh, with a previous event's legacy lying around.

Cheers once more,
Arie

+++ +++

Dear all,

I tore my sparse hair out, since I got nothing triggered on IRP.
Previews (IRP A and B) looked ok, cues seemed to get saved, but playback just gave a black picture.
No error messages, either.

What helped me:
I picked a different folder, to save IRP data (video, xml) in.
My guess is that the folder contained 'old' xml (previous / beta? versions of vMix), which somehow threw off the current vMix version.

I could imagine, that "just" deleting the xml in the old folder would have also solved the problem, but I didn't test that.

In sum:
not getting IRP to play back?
Try saving the IRP-files in a brand-new (newly created) folder, and for good measure, delete the old folder (both contents & folder itself).

Of course: make back-ups first !!

Good greetings,
and Happy 2016 (let's hope it will not be a replay of 2015)
Arie