Please refer to section 8.8 Integrated Interchip Sound Interface of the FX3_TRM.pdf document available in the SDK path: C:\Program Files (x86)\Cypress\EZ-USB FX3 SDK\1.3\doc\firmware\FX3_TRM.pdf.
The above section mentions about the working of the I2S block of FX3 and all the respective conditions and interface definitions.
Also, on Page no. 194 of the above-mentioned document, mentions the following about MONO channel(highlighted in Yellow):
This means that both the endpoints need to be present and must have data for the hardware I2C transceiver to start working(highlighted in Blue).