You can read tons of posts on various websites and pages about the issues with iPhones and StreamVision. I haven't seen an issue with it not playing the video back, once it is downloaded but my guess is the video isn't 100% downloaded and thus the issue.
StreamVision and iphones are notorious for having issues. The main issue is connection. The second issue is Pulsar for some strange reason chose the .avi format for their video format. Apple products don't work well with .avi files. In addition, the sound from your videos will not play natively in StreamVision on an iPhone.
For connection issues, many people claim if you Turn off locating option under Privacy in settings and turn off cellular data then open app, it helps. It seems to help some but I still have issues. Virtually no issues on Android.
For sound issues, you have to use a different app for sound. I have used iConv in the past but don't currently use an apple product with StreamVision any longer, so not sure.
If you plan to use StreamVision a lot, do yourself a favor and pick up an Android device of some kind. It will cause you a lot less frustration.