The OP highlights the miseries of socialism. It is a reminder that should be made often. Despite its murderous history, there are some, especially the young, who are drawn to socialism and wish to transform society accordingly. They should be educated on why their utopias are nightmares.
While I agree that socialism is a poor economic model, Venezuela's current problems started with low prices for oil and basically end with low prices for oil. I have to remind all of these Venezuela's socialism sucks threads this, along with the fact that the previous government, a Milton Friedman approved, neoliberal, oligarchical run government and economy did much worse when the price of oil dropped much less relatively, and is the reason why the country voted in a socialistic government. Venezuela stands as solid proof that extremes like socialism on the left and the neoliberal fantasy of the self-regulating free market on the right are to be avoided at all costs.
Q) Why does low oil price cause shortages of bread?
A) it doesn't
You get bread by growing wheat, milling flour, baking bread. Given there appears to be demand for bread, we are only left to wonder why there is no supply.
Except we know, don't we? Government has inserted itself into the market for bread and destroyed it.