Ethnic Chinese in Russia officially numbered 39,483 according to the 2002 census. However, this figure is contested, with the Overseas Community Affairs Council of Taiwan claiming 998,000 in 2004 and 2005, and Russian demographers generally accepting estimates in the 200,000–400,000 range as of 2004. Temporary migration and shuttle trade conducted by Chinese merchants are most prevalent in Russia's Far Eastern Federal District, but most go back and forth across the border without settling down in Russia; the Chinese community in Moscow has a higher proportion of long-term residents. Their number in Russia has been shrinking since 2013.
The article does not explicitly provide a definitive reason for the large discrepancy in the estimated number of ethnic Chinese in Russia. It mentions that the official census in 2021 recorded a population of 19,644 ethnic Chinese in Russia. However, earlier estimates from different sources have given varying figures, with the Overseas Community Affairs Council of Taiwan claiming 998,000 ethnic Chinese in Russia in 2004 and 2005, and Russian demographers generally accepting estimates ranging from 200,000 to 400,000 as of 2004.
In some cases, political pressure or interference can affect the accuracy of census data. Governments might manipulate or suppress certain demographic information to maintain a particular narrative or to support specific policies. Anyway, there seems to be a set of reasons and the article doesn't expand on why there's such a big discrepancy.