Today I proceed to post my usual weekly "update" to a respected "Ad Board Site".
0n my Profile in red letters is a notice:
"Effective immediately, all USA Profiles will be deleted"    

Including reviews and websites. Hope this helps…

It might not be anything "new" from outside (LE) pressure. It might be due to something totally "old" and internal to the company itself. Maybe there was a change in ownership or management (like Musk and twitter) and somebody thought, "Let's tighten this up to avoid and possible problems before they happen." (And if it's like Musk and twitter, you know what THAT means: makes things worse for their business.)
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Maybe you can post to the Legal Board abd see if anybody there knows what's up or might be up.

Another thought. You didn't mention the specific ad board site, but did you search other ads on the same site? Are the ads "normal" or are they also covered with the red banner warning?  
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Is there a chance that the website has been hacked? ... somebody hijacking their site and expecting to be paid a ransom? ... I'd suggest trying to contact the website Admin, but if the hackers hacked the Admin account, that won't work.  
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Do you know any other Providers who use that site?

Thank you Sir or Madam,
I wasn't referring to TER, however another site which I'm not sure
I'm allowed here on TER to mention said board.

Good thought thank you!  I'll post to the "Legal Board  
to inquire.
Getting ahead of the possible eventual shut-down, is a
plausible explanation.

Indeed other USA ads on said site have a "Deactivated" banner listed on their
profile.  
I queried the site's admin. however haven't heard back yet.
Hacking is also a possibility as you discussed, thank you!