Can you give us more details about your video mapping?
On some hosts, especially MacOS and some versions of Windows, requesting a specific resolution and frame rate is hit or miss. So you run into problems when you have several video mappings with the same output resolution but different frame rates. Note that internally in JeVois we detect duplicate output resolutions and frame rates and we adjust the frame rate down by 1fps when we find exact duplicates. So having lots of video mappings with similar output modes should in principle not be a problem, except that some host OSes have difficulty with it.
You could also edit your videomappings.cfg file in JeVois Inventor and delete everything except your module. This would help confirm whether this is due to conflicting resolutions or some other problem.
Another question, why do you use task manager to close the inventor? You should be able to just close the window. Some low-level video drivers get upset when you close uncleanly.