It sounds to me like the app is picking up the F1 overtone on the floor tom. If you put it in Spectrum View mode you'll probably see another peak at about 100-120 Hz, which will be the floor tom's fundamental (F0). It means that there is a lot of ringing F1 on the drum (which you may or may not like the sound of), so you may even want to dampen the outside (or use a head with damping within) and that will make the fundamental stand out more.
When you hit the drum harder you will excite the F0 perhaps more likely, so I'm not suprised its jumping between 110Hz (F0) - 140Hz(F1).
Actually as you hit the drumhead harder it causes stretching of the head, so its not unusual for higher frequencies to be observed when hitting harder (like a guitarist bending his string to raise the tone a little).
Hope that helps, feel free to let me know how you get on or email me at email@example.com