Why is old content of my website reappearing in Google SERP?

[Gilgue]

Two weeks ago, I uploaded new versions of my website pages with a FTP client. Since my site is almost 13 years old and I use to do it once a month, a week ago, googling some terms, I saw that the content was updated. Yesterday, however, I googled the same terms for a specific page and the old content showed up again.
What could cause this? Is there a chance that this page (at least) is somehow compromised? Any clues? Thanks in advance. P.S.: I live in Brazil.

[g1smd]

Yes, that happens a lot.

Google hangs on to old versions of pages for many months (this used to be called the supplemental index) and can continue to return a page for search terms that no longer exist on the new version of the page. The effect can come and go for a few weeks or more.