Just noticed the same silence issue again while using Cubasis with bs-16i app as AU inside Cubasis on 3 separate tracks along with a few other Cubasis instruments. For a 3 minute song, it recorded the actual 3 minute song PLUS another 6 minutes of silence at the end (recorded a total of 9 minutes duration). No other plugins were used except for the built-in Waves Ultramaximizer on the master track and native Filter and Spin FX effects on one of the bs-16i tracks. Also, noticed that while mixing down, it got stuck at 50% for a long time but finally finished mixdown fast (this fast section could have been the silence part).
Apparently, this is a Cubasis issue as it happened with Kauldron too - as reported before.
Using the latest version of Cubasis on the latest version of iOS on iPad Air 2.