Hi!/\r\n/it seems to me that the bit numbers on the protocol sniffer page in xscope, are supposed to be?numbers 4 to 7.
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from the manual:

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I can't tell if the SPI sniffer is actually working properly, or what logic channels are actually used.

The correct pins are 4 through 7. The SPI sniffer needs all 4 signals to work. Are you using the SPI select (/SS)?