They screw up very frequently. Sometimes maliciously, sometimes through incompetence, sometimes both. I can't convey the depth of this in a small comment box, but there's abundant evidence around on this topic if you care to look.
Overall, even when you're talking about legitimately designated authority given to a person ... it's VERRRY easy for a human being to screw up and get it wrong, and it has huge impact over the lives of their targets. Needs to be approached by the authorities with extreme caution. In practice, probably many of them aren't aware of the weight of their actions, or don't care.
Do you have a source for that? Frequently is a relative term. 1,000 fuck-ups can be a lot or a little depending on the total number of interactions we are talking about.
These don't include number of cases where legal action wasn't taken or which got thrown out due to qualified immunity (these are somewhat related, if case is unlikely to get past qualified immunity it's quite unlikely legal action will be taken). And probably cases which actually went to trial as it seems to focus on settlements.
Additionally there is for example https://www.nyclu.org/en/publications/cop-out-analyzing-20-y... which covers 2000-2020 misconduct complaints. According to it disciplinary actions were taken 4283 times, meaning that even if conduct was enough to reach settlement it doesn't necessarily mean it results in any actions taken against the officer.