When you say that shutting it down cures the problem, does it then run the conventional engines at proper speed? Sounds like a bug in the app or DCS version.
What version of DCS is in the TIU?
Has the pro app updated itself? ( are you on home network or MTH?)
I don't run any conventional thru the TIU, so I'm not really familiar with what you're seeing. I have seen recent posts of problems using the app and the variable channels. So maybe someone with experience will chime in here.