I haven't looked at the reason yet; so someone else may be able to comment further...
The weather is particularly warm right now, hence why there are alot of faulty trains/points failures etc as they are more susceptible to fail during extreme weather. In particular points which aren't used that often are prone to fail even more. I heavily suspect the heat played a role in the suspension.
Note the Victoria runs an extremely intense service every 90 seconds...
Not been a good week for the Victoria line!!