I recently checked my Trash folder in Gmail. I had emails in there that were several years old, right below the text that says Gmail deletes emails in the Trash folder older than 30 days.

Indeed, a quick search suggests that spam is automatically removed every 30 days there. The wording was "Google hid it from me", so either I have wrongly assumed that it's about the spam folder, or it is possible to disable autoremoval.

Edit: or, as the sibling comment suggests, it behaves strangely with respect to removal as well.

Or user accidentally archived it. “X did Y” is often a user’s way of saying “I accidentally made X do Y” without having to accept blame. It’s the “dog ate my homework” of excuses.

Another instance of Google being user hostile?