I believe that the Leader of the Opposition, has realised (like many in the UK) that there's a line, albeit somewhat blurred, between the correct message that Black Lives do Matter and some of the proposals / ideas put forward by sections of the movement itself which are not realistic.
While I have sympathy for some BLM defund the police situations in the US, in the UK the reality is very different. Corbyn was all for increasing police at the last election (circa 10,000 IIRC). The reality is that the UK police force is underfunded rather than "militarised", UK police have too much paperwork to complete to be out on the street and there's a comprehensive review whenever a police officer fires their weapon.