MCP3008/ADuM3154/ESP32 - Corrupted MISO Data Line
Complete facepalm here, I totally missed the pullups on the CS lines...

I had read on page 17:

To allow compatibility with nonstandard SPI interfaces, the MI pin is
always active, and does not tristate when the slave select is not
asserted.


I had assumed that this also applied to all the pins including the CS.
I also thought the MCP3008's had CS pullups too. Not sure how I missed this in the scope, the CS looked good but I didn't realize the other 2 MCP's that I was not probing were driving the MISO line low.

From page 18:

Figure 12 illustrates the behavior of the SSA0 and SSA1
channels. This diagram assumes that MSS is low and that SS0,
SS1, SS2, and SS3 are pulled up.