Would appear that Hilton is back on Topcashback in the UK. Only quotes one rate of 4%. Often used to be hit and miss as to whether the cashback arrived in my account but will give it a try again.
Hilton was indeed one of the worst at not paying out the commissions promised.
Topcashback USA has Hilton back as well, but still with the 1% rate for elite members and a long list of excluded hotels.
So I would assume for now that Hilton has no real intention of paying 4%. Of course, there's no harm in trying TCB UK and seeing how it goes.