So far in 2020, four House incumbents have lost renomination to their seats (five if you count New York Democrat Eliot Engel, though absentee ballots in New York haven't been tabulated). But there are ... differences between what causes a Republican and a Democrat to lose their own party's nomination.
For example, Rep. Dan Lipinski (D-IL) was one of the most conservative members of his caucus -- opposing abortion rights, gay rights, and Obmaa care -- despite representing a D+6 seat. If you're wondering how he got elected in the first place, the answer is that the seat was previously held by his own father who -- in classic machine fashion -- won renomination and then announced his retirement, inducing the local party to hand the nomination to his son. He was defeated by Marie Newman, who narrowly lost a challenge in 2018 and by all appearances is a perfectly normal Democrat. This is not at all abnormal.
Contrast that to what happened last night, where Rep. Scott Tipton (R-CO) was stunningly unseated by conservative activist Lauren Boebert. Nobody had the race on their radar because Tipton, who enjoyed Trump's endorsement, hardly seemed to have committed any sins against the conservative movement which would generate primary opposition (The Onion notwithstanding). So what was it about Boebert which caused her to surge to victory? Well, she's a qAnon-endorsing conspiracy theorist whose main claim to fame is running a bar called "Shooters" where the staff openly carries guns and which defied orders to shutdown in the midst of the coronavirus epidemic.
Of course, it's not always better when the incumbent loses because of their apostasies -- particularly when one considers what counts as "apostasy" in the modern GOP. Rep. Denver Riggleman (R-VA) also enjoyed Trump's backing, but lost renomination in a "drive-through convention" to far-right challenger Bob Good. Riggleman's wrongdoing? He officiated a same-sex wedding for two of his former staffers. That's enough to get you bounced in the 2020 Republican Party.
But I guess Republicans did manage to dislodge their most openly White supremacist member this year -- so good on them for that.