Hi!
Unfortunately, idMatcher is a bit unstable and we don't have the resources to maintain it properly. A trick you can use is to do the job with idTracker itself: Rename your two videos with the same name followed by consecutive numbers (e.g. video1.mp4, video2.mp4), so that idTracker believes they are a single video. Then, it will extract a common set of references for both videos and will track them both with the same identities.
The tracking quality may be lower than the one you would obtain using idTracker on each video and then idMatcher, so you may want to also track each video separately (although you may also get high enough quality from the common tracking, it depends on the video characteristics).
I hope this helps!
Alfonso