The first one that seemed removed was actually moved to a thread talking about 2fa. It seems it's more a matter of consolidating multiple threads on the same topic into a single thread. Which makes sense.
If anything, it's a failure to use a 301 moved permanently header.
At a former company (which has since gone out of business) I met some people who loved Evernote.
One was an administrator who cheerfully kept confidential details about the security of our corporate network in it without once reading the Evernote TOS or considering the consequences if those TOS changed.
Even after I explained that those TOS clearly violated several parts of his employment agreements, he continued to use it. He didn't think there was anything wrong since our CFO also kept a lot of sensitive information in it...
Hmm.. As a site owner I try not to jump to conspiracy conclusions, as I've certainly been on the receiving end of enough of them due to random coincidences and such. That said, this does indeed seem odd. Did you try posting a question in their forums about it?
Me also but have regularly checked their 2fa threads because it's a feature I'm interested in so was surprised to see them gone so soon after the hack. As you say, could be unrelated.