Autorevert works by polling the file-system every
auto-revert-interval seconds, optionally combined with some event-based reverting via file notification. But this currently does not work reliably, such that Emacs may revert the PDF-buffer while the corresponding file is still being written to (e.g. by LaTeX), leading to a potential error.
With a recent AUCTeX installation, you might want to put the following somewhere in your dotemacs, which will revert the PDF-buffer after the TeX compilation has finished.
(add-hook 'TeX-after-compilation-finished-functions #'TeX-revert-document-buffer)