So I was having the same issue (debug print not showing in VIVE, and prefer so see the message on-screen instead of having to sift through the logs).
The reason is that the lines are printed “out of sight” for both the HMD and the preview on-screen.
A simple workaround is to make a loop to print some random lines before you print your actual message (see screenshot). The magic number seems to be 28(!) lines.
