I feel like a challenge so I'm going to play the devil's advocate. It is possible to craft explanations for why UFOs behave this way, if they are in fact aliens. There's a very common fallacy in a lot of alien debunking discussions. It goes like this: if you can travel faster than light then your technological powers are entirely unlimited and you can do whatever you want. There's an implied assumption that FTL travel is a sort of über-technology and the speed of light is a kind of ur-limit. Once you know how to break it, every other physical law becomes breakable too.

There's no logical reason to believe this is the case. It's a social assumption caused by the fame of Einstein and the way pop culture has constantly told us FTL travel is "impossible", putting anything that can do FTL immediately into the realm of "if you can do one impossible thing, why not N impossible things". But C being the universal speed limit is a theory only 115 years old. That's not very long in the grand scheme of things. And now we're seeing respectable and serious physics research that explores the concept of a warp drive. Whilst still in the realm of impossible, it appears there are gradients of impossible and FTL travel may slowly be moving between them.

What if FTL travel is easier than we think? Then a civilisation that mastered it would not be some unimaginably advanced god-like race about whom we can assume nothing. It would be a civilisation kinda like ours, just with FTL drives. And we could then start to apply everyday reasoning to their behaviour. For example, why would UFOs fly around and yet be detected by radar/cameras/sensors etc? Well, maybe:

• Complete invisibility is not a tech they have. Our stealth tech is not entirely stealthy, just stealthy enough to get close against currently existing radars.

• Their FTL drives are incompatible with the type of ship geometry required for radar invisibility.

• Their knowledge of our own sensor capabilities is old/not entirely accurate, so they can hide from sensors but don't always do so at the right times. E.g. it may have impose some energy or tactical costs to hide so they don't want to do it all the time.

• They don't actually care whether they are detected or not.

• They do in fact have invisibility technology and there are shit-tons of UFOs flying around that we don't detect, but because they're not an uber-race they make mistakes just like we do and occasionally this results in sightings that shouldn't have happened.

Why would they not make contact? Maybe:

• They don't wish to because we have nothing to offer them.

• They don't know / can't agree on which political bloc to make contact with, and are waiting for humanity to unite under one world government (hopefully not).

• They have some rules against making contact unless some galactic federation votes that it should happen and the votes hasn't yet been won, but information is being collected by survey craft to inform the decision making progress.

Why would they apparently rejoice in doing ludicrous or pointless changes in speed or direction?

• Why not? If your FTL drive lets you change direction without needing to worry about gravity, why would you ever turn in a curve?

• Maybe they are frequently retasked and need to go somewhere different to their original goal, especially when they believe they were detected?

And so on. The thing is, if you're willing to make just a slight leap and assume that FTL tech is not as hard as we think, then it's suddenly easy to come up with lots of explanations for UFO behaviours. It's only the social assumption of (FTL->any imaginable tech) that makes us ignore these possibilities.