I sent an email to a filtered Data Extension that contains a PersonAccount (the PersonContactID is related to the subscriberkey) but I don't see that email tracking in the profile of this Account in Salescloud. The email was delivered and opened.
In addition to what Rain said, this can be caused by:
1.In journey builder while configuring your email send, did you check the checkbox for send tracking back to salescloud?
2.Expired token on Sales Cloud: When you go to Marketing Cloud in Sales Cloud, are you redirected to a login page where it asks to connect your Marketing Cloud user? If your answer is yes, then the token expired, you will need to connect your Marketing Cloud API user again.
PS: you need to logout from your Marketing Cloud account before trying to Connect your API user on SalesCloud. Otherwise, this user will be used as an API user.