Perhaps you are getting the issues mixed up. Corbyn blaming the West/NATO for being the cause of Putin's aggression ahead of the invasion did nothing to help and smacks of political grandstanding, at a time when a non partisan approach may have been more tasteful and useful.
That is a separate issue to Corbyn being against the war (who wouldn't be!). If Corbyn is so anti Putin why was he acting as his apologist in the run up to it - apportioning blame elsewhere. In order to push some cheap political sound bytes for his own warped ideology I daresay.
It served no useful purpose and was basically all about Corbyn's personal hatred for the West. Some things should be above ideological political profiteering by individuals and this most certainly falls in that bracket.
Fact - It wasn't NATO that invaded the Ukraine, whose legitimate choice it is to look towards the West and reject Russian authoritarianism for their democratic future if they choose to do so. There is only one problem here and that is Putin's refusal to respect that Ukraine democracy in practice. Corbyn should have called it as it is, if he is such a fierce critic of the man he claims to be. Corbyn can't have it both ways without being criticised for the hypocrite he is.
As previously discussed on this thread, Corbyn et al are strange bed fellows with Farage on this score. It does not reflect well on any of them.