We can not check the problem accurately because there is no sample file, but it seems to be caused by the difference of the CPU specification of the device when it is played with software decoder. Because software decoding is software installed on the device, playback performance may vary depending on the CPU specifications of the device.
The Chromecast's playing principle is, if nPlayer sends a file to the Chromecast, playback is done by the Chromecast. Chapters are not activated because Chromecast do not support it. Please take considertation into this.