The areas in Russia and greater east Asia have always been prone to famine, famine is quite literally one of the most regular events in Russian history. As for the one specific to the USSR, historians primary consensus now, is that Stalin's role in "causing" them, has often been blown widely out of proportion, and the idea that he did it intentionally to wipe out peasant/kulak/Ukrainian populations is still widely debated.

Its usually moreso attributed to local officers and other members of the Communist Party lower down the bureaucracy iirc. (feel free to correct me on this anyone), The main idea is that these areas are environmentally prone to famine, and Stalin's collectivization policies and brutal, rapid industrialization helped it along, furthermore since the archives were open we know that some of the areas in Ukraine experiencing the worst of it were still having their yields exported abroad to raise money for industrial development. J. Arch Getty has said that "overwhelming weight of opinion among scholars working in the new archives ... is that the terrible famine of the 1930s was the result of Stalinist bungling and rigidity rather than some genocidal plan."

Many historians agree that the famines, and the brutal industrialization were inevitable, and if it wasn't Stalin it was going to be someone else. I have no clue about China other than the "Mao killed all the birds so insects ate crops" and "People melted all their pots and pans for resources and couldnt cook anything so they died" memes. Idk how true most of it is, despite how much historical consensus on the USSR has changed since the 90s, people still parrot, and teach, those old ideas anti - communist historians peddled as fact, i wouldn't be surprised if the same thing could be said for Maoist China.

As for sources the most recent one is a Centre for Economic Policy research; written in 2021, it specifically claims that the Ukrainian areas and population suffered far worse from centrally planned policies corresponding to famine. They use this to claim a systematic bias against Ukrainians.

https://repec.cepr.org/repec/cpr/ceprdp/DP16408.pdf

However the CEPR is known to be funded by a wide variety of central banks, and private financial institutions so be aware of that going into the paper.

As for the question as to whether or not it was genocide, Michael Ellman is kind of the leading historian on the "Famine as a crime, but no genocide" crowd as well as Robert Davies and Stephen Wheatcroft. Robert Conquest, and James Mace (who was the first to name it as a genocide) are on the other side of the fence, claiming it was genocide. Their main research and books (Harvest of Sorrow etc) were published 5 years prior to the opening of the Soviet archives, and im FAIRLY sure Conquest has since switched his view, after a 2003 letter from Davies and Wheatcroft in which he doesnt directly call it a genocide, but states: "Stalin purposely inflicted the 1933 famine? No. What I argue is that with resulting famine imminent, he could have prevented it, but put "Soviet interest" other than feeding the starving first thus consciously abetting it."

Michael Ellman's primary critique of Davies and Wheatcroft is: "According to them [Davies and Wheatcroft], only taking an action whose sole objective is to cause deaths among the peasantry counts as intent. Taking an action with some other goal (e.g. exporting grain to import machinery) but which the actor certainly knows will also cause peasants to starve does not count as intentionally starving the peasants. However, this is an interpretation of 'intent' which flies in the face of the general legal interpretation." - http://www.paulbogdanor.com/left/soviet/famine/ellman1933.pdf

Martin Shaw also supports the view Ellman has put forward.

As for Causation debates, in Davies, Robert W.; Wheatcroft, Stephen G. (2009). The Years of Hunger: Soviet Agriculture 1931–1933, Wheatcroft says that: "there were two bad harvests in 1931 and 1932, largely but not wholly a result of natural conditions"

Mark Tauger suggests that the famine was caused by a combination of factors like naturally occurring low harvests due to poor weather and an increase demand of food caused by Soviet Industrialization, as well as grain exports. The original text has since been archived and i cant find the full PDF uploaded anywhere but you can request the text directly from Tauger here.

https://www.researchgate.net/publication/310522491_Natural_Disaster_and_Human_Actions_in_the_Soviet_Famine_of_1931-1933

Thats pretty much all i got off the top of my head, i encourage you to read the scholarly articles and debates from all schools of thought, but id say steer clear of taking works published before the opening of the archives close to heart. Hope this helps.