Is the skeptics close reason "Under current investigation" the same as our "opinion based"?
As a point of order, the globally available (i.e. not side-dependent) reason used to say "primarily opinion based" not so long (days) ago. The global close page reasons have been "touched up" the company quite a few times. There's an answer on the big meta complaining about the recent change that dropped "primarily".
And there are a bunch of Skeptics pages where they motivate their custom close reason, e.g.
Should issues from today's newspaper headlines be left open? This is a separate issue.
Where there is an unsubstantiated allegation in the media, and the journalists are rushing to find the answer and be the first to report it, there is nothing that Skeptics.SE can do. We don't have an army of investigative journalists that can interview people. We don't have an army of detectives with badges that can search premises. We don't have an army of prosecutors that can compel people to answer questions at risk of perjury. We don't have an impartial jury to decide on issues of fact.
Such questions are closed until they can be answered by referring to other sources (by which time the OP will probably find the answers have already appeared in the media).
And older discussion where that was apparently decided, which has more votes.
Now since in some of your other comments you referred to (presently unanswerable [for certain]) Covid-19 questions... alas the relaxation of the rules has taken place in that respect on Skeptics too. These are not all medical questions, but arguably may contravene their "under investigation"/recent-events rule
Most of these don't have good, definitive answers and they aren't even about medical science... just related to the Covid-19 crisis. So yeah, what the Skeptics rule book says and how they enforce it in re "under investigation" stuff is quite far apart. The mod who had pushed (hard) for that rule has resigned in the meantime.
I've only found one Covid-19 q closed as "under investigation" (there might have been more but this one has positive score, it was't quickly deleted.)
Some similar ones about discrepancies on uncertainty datasets were not closed though. And some (eventually) even got some good answers. E.g.
So it's not always obvious when such (Skeptics) questions should be closed. I'd grant you that the more proper medical (science) questions of that kind probably aren't so easy to clinch.
And I found another closed q, from way back in Jan. This was closed twice (so reopened once). The (Jan) answer starts with "It is too early to tell."
There's one more q that was not reopened [probably] for this reason ("under investigation")
This was closed as "not notable" (including by me), which means the question lacked a quote (usually needed for a Skeptics q). A quote was later added, but the mod did not reopen the q and commented "Finally, this is probably too early. Come back in a few months when the analysis of the Italy situation is complete."
So there are some Covid-19 questions on Skeptics that were indeed closed clearly or probably with that "under investigation" reason (as a contributing factor)... but they are frankly dwarfed in number by similar Covid-19 questions that were not closed.
And to exemplify for contrast a q that was (properly) closed as [primarily] opinion-based:
If you want me to theorize what should be closed with one reason and what with the other...
"under investigation": the q could potentially have a fact-based answer, but those facts haven't been yet established, yet are likely to be so at some point (in our lifetimes).
"(primarily) opinion based": the q revolves around some value judgements that even if they involve [even well established] facts, we know is likely to still receive different answers e.g. based on how one weighs certain criteria/objectives against each other.
"Opinion-based" is a network-wide close reason; Skeptics has it, too.
Additionally, sites can have a limited number of site-specific close reasons to cover common categories of questions that the community has decided are not on-topic. The "under current investigation" reason is one of theirs.
Sometimes close reasons overlap; I think that yes, sometimes we use the "opinion-based" close reason to close questions that are speculative and therefore cannot be answered. On Skeptics the same sort of question might be closed as "under current investigation".