"Mysteriously". The gadget is pushing fifty with vintage hardware in a hostile environment. One could say a 90 year old grandma was asleep, presumed dead, and when the paramedics showed she woke up with, "What's all the fuss?"
At the same time, every component and line of code is known. Presumably they can simulate and test for all sorts of crazy exotic problems and error cases. It’s surprising that they’ve hit a new type of problem.
On the one hand, it has crashed into a lot of somethings—like cosmic radiation and micrometeorites. On the other hand, there is a lot of space in space, and the chances of Voyager crashing into something of the same or larger scale as itself is infinitesimal.
A big unknown planet has crossed the path between Voyager 1 and the Earth, blocking the radio signals for 2 days !
(This is not impossible, because a planet so far away would have an extremely low angular velocity, so an occultation could take so long even for a not very big planet.)