I'd argue these developments would be most interesting, and justifying of a warning beacon, or even some kind of a barrier, were such behaviour to be detected as originating from an uncontacted species.
The jury is still out for me on UFOs, even with all that's come to light. There's something there..but occam's razor would indicate it's not aliens. Still, IF it was then there's a correlation I find interesting.
The number of recorded UFO sightings (whatever the cause) was minuscule before WW II. Looking at www.ufoevidence.org (not exactly peer reviewed, but it's there), the pre-1940s cases number 12. The 1940s hav 20. The 1950s have 64. The 1960s have 92. 1970s 131. Then it curiously drops in the decade the Soviet Union fell and nuclear war became less likely. 1980s has 58, 90s 59, and only 118 from 2000 to 2020.
If UFOs exist and are aliens, then I don't suspect they are visiting us for some altruistic purpose but for research. After all, if our scientists had the chance to see a pre-industrial race on the verge of collapse or advance, like the Mayans just before meeting Cortez, our scientists would jump at that chance. And there is the Fermi paradox - maybe most species kill themselves off and aliens want to observe to form theories on why.
This is good, to be clear about what assumptions we are making. I see 'UFOs are real/UFOs are alien' as one not two and would call it a premise more than an assumption. If _, then here's our plan...
As for the 'not alien enough to make us unable to reason' cuts both ways. The opposite is the assumption that they are similar enough that we can reason about their behavior. It's important to cover both sides of this one.
The biggest assumption is the degree of their interest in interacting. I would place this at low. It's hard to come up with why this might be low: prime directive, we're an inconsequential species/or one of vastly many, reaching us is costly, etc.
Assuming they exist is central to exploring this context. This doesn't mean anyone exploring the idea necessarily believes or disbelieves they exist.
There were a bunch of ex-military who testified publicly as to UFO events surrounding nuclear facilities in the US and the former Soviet Union around the cold war. The UFO's were reportedly deactivating missiles on both sides simultaneously.
I don't recall the source exactly but I'm sure it's out there. Anyway, it at least makes some sort of sense (versus other claims about aliens sticking things up peoples butts).
I mention it as if this happened, and was some kind of intervention, and presumably successful, it might make sense they subsequently laid low for a bit, potentially matching your correlation.
Again, I'm not suggesting any of this is real, it's just an interesting idea within the context of this post.
And if those nuke produced some currently undiscovered very far (light years), detectable energy / event? Yeah, most close neighbors could have already spotted us in 1950.
Our extensive radio transmissions would surely already have been received, but the nukes (being secret initially), if detectable at interstellar distances, could certainly give away destructive capability earlier than radio transmissions could reveal.
The only thing that does makes sense is that the only time to even consider aggression is if we were closely matched which has negligible likelihood.
Or perhaps we should quickly figure out what constitutes as 'cute' or 'entertaining' to our visitors, if we are to model their behavior to our own.