I have an Innova and am very pleased with it, but do occasionally have tension issues. Usually due to a blob of lint getting stuck in the bobbin case spring. But tension going off mid bobbin like you describe, really makes me think your bobbin winder on the machine is not winding properly so you are getting bobbins that are not wound with a nice even tension, too loose and too tight in places.
Just for the fun of it, why don't you try investing in some prewound bobbins and see if the problem persists. I am a great fan of the magna glide bobbins from filtec
www.bobbincentral.com. The little magnetic core eliminates backlash issues as well (you need to remove the anti backlash spring in your bobbin case if you have one, should you decide to use magna glides). I rarely wind my own bobbins any more and my tension is constant right down to the last inch of thread on those bobbins. Now I have had some issues with some of Superior's prewound bobbins. They tend to go wacky the last 1/4 of the bobbin so I use those for sewing on bindings.