If I "assist it" just a little with slight hand pressure then shuts on the first trip down.
I (correctly or incorrectly!?) Deduced this to mean too much resistance in the drive system/ cables is triggered the perceived obstacles detection. Interesting others have had it apart, I thought of asking about stripping this down but assumed from Citroen perspective it's full motor + cables that get swapped (much like elec handbrake) so assumed there'd be no guide on disassembly of the unit into sub components.
I also get Economy Mode Active disabling the boot closing if has been opened for long periods. Manual coursing in this case then does get the catch to engage without issue - different to what reported by others.
Oh for a mechanical boot catch (linked to a mechanical button with a metal rod) and a pair of gas struts!!