Postpublished at 09:41 Greenwich Mean Time 9 February 2020
The explanation...
UltraEdge was not working for the Temba Bavuma review so the umpires have decided that South Africa did not lose their review, despite it being three reds on ball tracking. And not sure it should matter, given they did eventually check to confirm Bavuma didn't nick it.
That means Rassie van der Dussen had a review to use and was allowed to use it, despite not calling for it until he had basically left the field.
All very confusing and poor communication from the umpires. England can be rightly aggrieved.