is the section of Labour who are unwilling to move on from Corbyn.
I think you misunderstand their motivations. They don't have allegiance to Corbyn; he's just the accidental figurehead due to him being elected leader (because it was 'his turn' to stand as the token lefty in the 2015 leadership election)
There's a sizeable contingent of people in this country who are in that traditional mid-left-to-hard-left area on the spectrum, who in the 90's saw the only left-of-centre party of any size - the Labour Party - move from an economically soft-left-to-mid-left party, to one following a centre-right-to-slightly-left-of-centre economic framework (even adopting some Thatcherite & corporate-capitalist policy from the 80's & early 90's as non-negotiable)
In know so many people that felt that the only election options they had were reduced to a hard version of corporate-capitalism that pandered to the already wealthy and big business, or a milder version that sought to mitigate some of the worst impacts.
The election of Corbyn came out of nowhere. But it was driven by people wanting a change in the econo-political direction of the UK.
Those people have not gone away.
There's a compelling argument made by many that Labour is only electable if it embraces that economically centre-right-to-soft-left political space, that the party should adapt to fit what it thinks will win elections. That people should very much lower their sights in terms of what Labour could achieve.
But there's also an argument that political parties should stand for something core. And their objective is to try to convince enough of the electorate of their policies and arguments.
In reality, though, all that needs to be put into the context of many of the loudest voices in the current leftist movement are annoying idiots, with too many in that section of politics motivated by their zealous devotion to identity politics and extreme social justice issues. In their present incantation, 'the left' (if we characterize that by the Corbynistas and Momentum lot) are incapable of winning an election.