If devices are not shown in the app it can be an issue of the Android device or the USB device or a combination of both.
Automic start of this App and automatic driver selection is only supported for the well known USB VID/PIDs compiled into the app.
For other devices (e.g. exotic CDC devices like Digispark) you can select the driver in the 'USB devices' tab.
Some vendors do not enable USB host mode on some devices (e.g. Samsung S3 Neo).
You can try rooting or installing an alternative firmware.
If your device is rooted, you can try adjusting files in /system/etc/permissions manually or with one of the various USB OTG checker apps.
Android is not a real time OS. The thread responsible for receiving data might not be scheduled by the OS or garbage collection might be ongoing or …
Therefore data loss can happen for continues read at high baud rates. If data is lost, typically some smaller fragments in the middle of the data are missing.
For lower baud rates or non-continuous transfers this is not an issue.