TPS659037: TPS6590378 and AM5728: SMPS1/2 output is changing on I2C access timing

On the startup timing, when I2C access on several times by system side (AM5728), SMPS1 and SMPS2 output (AM5728 VDD_MPU input) voltage are changed at all such times.

 （ex. 1.2V→1.09V→1.06V→ 1.2V→1.09V→1.06V…）

Is these voltage changing are assumed normal operation?

If abnormal operation, please let me know any idea for measure.

・Waveform; Blue is I2C signal and access timing, Yellow is SMPS1/2 (VDD_MPU)

・TPS6590378 schematic; red point is measured point.

・This question is accompanied by below processor thread. we hope advice from the viewpoints of the PMIC side, too.

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1012960/am5728-voltage-change-of-vdd_mpu-at-start-up/3754986

Best regards,

Satoshi