Can you please try using RTCC_I2CMasterSendRestart() API instead of Start API and let me know if that helps?
You can refer to the component datasheet for information regarding the API. Additionally, you can use the CE222306 - PSoC 4 I2C Communication with Serial Comunication Block (SCB) as a reference.
Hope this helps,
Thanks and Regards,
Rakshith M B
This was the magic I needed. Wasn't sure when to issue a Start vs Restart.
Glad it helped!