It’s a very good security practice that you pay attention to the warnings you received. 
With that said, the advice irvinewade posted is worth following, namely that your update may have changed the grub files (to include a new kernel perhaps), and with the new files a new file checksum may have been created. Checksums are used to detect tampering but may also detect legitimate changes to files as well since legitimate changes will affect the checksums.
It’s wise to double check things as you’re doing.