I guess this is not a roll bar issue as such ??!!
The act of placing the top harness mounts on part of the roll bar structure, brings this into the area of: Seat belt mountings, structure & security !!
In this case, one can only assume that in the examiners view. the upper seat belt anchor point & it's associated structure was deemed unacceptable & lacked integrity or strength in a critical area
One thing to bear in mind is ..... Not all of the IVA requirements are set in stone.
As with the humble MOT test .... A lot of rules & regs are open to the examiners personal point of view as to how they should be implimented .... This is probably suplimented by memos from individual station managers, VOSSA head office & the department of Transport
I expect any MOT tester will tell you that it's not an easy job .... Dread to think how the IVA examiners cope !!??