The things I’ve heard are that the OAS, the Organisation of American States, has a history of giving passes to suspicious right-wing elections, while scrutinising above-board leftist wins. That is the organisation alleging irregularities that lead them to suspect meddling in the election. I’m struggling to find the paper again, but there was an analysis from another group showing no irregularities, and suggesting that it makes perfect sense that the later ballots from more rural areas (where Morales is more popular) would take him over the cutoff for a second round. I have not seen any links to the analyses that the OAS presumably did, and have seen accusations that they have no basis for thinking the results are in any way irregular.
Morales has apparently had a two-term limit instituted during his first term, had a second term, had a third questionably-valid term during which there was a referrendum about officially enforcing the term limit. The public voted against allowing more than two terms, but the supreme court ruled that there was no consitutional basis to do so and allowed Morales to run for a fourth term. I have heard that the supreme court is elected, and so it’s not as suspect as it otherwise might be. Morales ran for a fourth term, and the results say that he won in the first round. The OAS disputed those results, and Morales agreed to a second election to confirm the result, but the military forced him to resign before that could happen.
EDIT: Correction and addendum, he agreed to an OAS audit of the results. Worth noting that his opponent in the election did not.
It’s worth noting that there have apparently been twenty days of protests against the results before he resigned. I have seen accusations that Morales’ supporters (and employees?) instigated violence against a university (or more than one?), including raping a number of women from those universities, but I don’t speak or read Spanish so I haven’t seen more detailed reports about that, it’s much easier to find information on the election stuff in English.
Morales was apparently involved in nationalising natural resources, including lithium, that the US would like to have access to and have a much better chance of securing with a non-leftist government. And the US has a history of backing coups against socialist leaders in South America. He’s also indigenous, and reversed a trend of minority white Bolivians holding the majority of governmental offices, from what I’ve read. There have also been accusations that the opposition party has been in frequent communication with the US, presumably to an unusual degree? But I haven’t looked into that aspect, it seems like a difficult thing to verify.
All of this is what I’ve gathered from twitter, so huge grain of salt. But it seems like there are legitimate greivances with Morales’ conduct, and also that he won an apparently fair election, was willing to have those results fully audited by an outside body, and was then forced to resign by the military.
Definitely look into it yourself, I only speak English and I’m British, so the information readily available to me is limited and coming through a lot of biases.
EDIT: https://twitter.com/kevinmcashman/status/1193703918624108544 This is the thread from which I’ve drawn a lot of this information, from an author of the paper which claims to show that the results are probable as well as possible.