Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
I have to admit my knowledge of the Schwinn line of exercise bicycles is not as extensive as it should be in order to advise you as well as I should.
However, your question was neglected for a while, I can see, and I thought it deserved an answer of some sort, at least.
If the tension releases, that is most likely to be a problem in the resistance motor controller board, I think. Problems with the resistance motor would be more likely to show up as complete and persistent failure of resistance in the pedals.
However, anyone repairing the machine, having opened it and unplugged it, would be well advised to check for loose connections or fasteners that are not fastened. And, to check the motor controller board for indicator lights.
Also, sometimes a motion sensor might be nearly out of alignment, and when the machine is vibrating owing to being used, that might turn into altogether-out-of-alignment. So motion sensor alignment should also be checked, even if only briefly.