IWR6843AOPEVM: Can't Pull SPI SCK Down to 0v

I'm running into some bizarre issues when using the IWR6843AOP as a SPI slave. I can't seem to pull the SCK line all the way down to 0v, and almost no communication transmits correctly. I've been able to mitigate the problem by using "high drive" gpio on the master which increases the current that it sinks. (Nordic Semiconductor - nrf52840) Here is what the signal looks like without high drive:

What I find odd as well is that the 3.3v rail has nearly a 0.5v ripple at about 270kHz. I suspect this is related to the errata regarding the power supply capacitors needing to be doubled up on this EVM. This is also what the SCK signal looks like without anything attached to it.

You can also see this ripple reflected in the SCK signal.

What on earth is going on here? Is there something wrong with my EVM? Are the pull-ups just really strong? I'm not even sure I it's the pullups since this code didn't seem to change anything:

Pinmux_Set_OverrideCtrl(SOC_XWR68XX_PINE13_PADAF, PINMUX_OUTEN_RETAIN_HW_CTRL, PINMUX_INPEN_RETAIN_HW_CTRL);
Pinmux_Set_FuncSel(SOC_XWR68XX_PINE13_PADAF, SOC_XWR68XX_PINE13_PADAF_SPIA_CLK);
Pinmux_Set_Pull(SOC_XWR68XX_PINE13_PADAF, PINMUX_DISABLE_PULLS);