I tried to culture Bacillus coagulans for 36 hours in my yogurt machine that is supposed to go to 115 degrees F. However, the peak temp reached was an only about 100 degrees. Is it safe to eat yogurt made at 90-100 degrees F with a culture that requires at least 115 degrees Fahrenheit? The yogurt looks thick and smells fine.
Yes, you should be fine. The range where B. coagulans thrives is listed as 30–55 °C (86–131 °F) with an optimum temperature of 50 °C (122 °F) (source). (Other sources claim slightly different numbers, but that’s irrelevant in your case.)
In short, at temperatures within the given range, the bacteria will still grow, only the growth rate is less - the father from the optimum, the more noticeable. I don’t think your temperature was so far off that there is a significant risk of unwanted bacteria taking over, especially if you did an initial pasteurization step and your results look a smell as expected.