Tool/software:
When evaluating the TPS25751, the default configuration had "GPIO Moisture Event" on GPIO1 and this functioned correctly.
To closer represent my previous design, I re-allocated the GPIOs so that "GPIO Moisture Event" was on GPIO11 (also on the pin header).
A change in voltage was NOT seen at the header. It appears that R74 links header to IC and this resistor is NOT installed, despite being shown in schematic.
No major issue, just paying it forward incase anyone has weirdness with GPIO11.
Simon.