In particular, the lack of a "status quo" option for Crimea (the referendum only had two options, go independent or join Russia) and the lack of international observers (OSCE observers currently in the Crimea were asked to leave by the Russian authorities in the area) made the whole thing iffy from the get go.
And that's not even getting into the fraud allegations ...
There was no status-quo option because at the time, according to the dominant legal opinion (as in, backed by force), Crimea had already seceded from Ukraine. To consider the status quo that Crimea was part of Ukraine would undermine the legal basis for a referendum without assent from Kyiv, which is why it was not included. It's for sure bullshit to the moral level, but it couldn't have been done differently while still being a referendum on joining Russia. They could have done a referendum on returning to Ukraine, I guess.
One problem with many mainstream outlets is that they are often give free passes to organizations like OSCE. For example, the OAS, an organization that serves a similar watchdog position in the Americas, completely bungled their duties in recent Bolivian elections. So much so, that they helped legitimize a violent far-right coup in 2019.
https://en.wikipedia.org/wiki/Holodomor#Aftermath_and_immedi...