I don't know how common it is, but I occasionally have that happen too. I think it depends on how backlogged the filtration servers are at the time.
If you whitelist email@example.com at priority level 6, and have @aol.com blacklisted at the same priority level, I believe the blacklist will take precedence. The solution is to set the whitelisted address(s) to 7 or higher. Alternatively, it could be that the email address in question is not in fact the same as the return path. Reveal the full headers of your email message (instructions vary by email client) and check that the return path header matches the email address from which the message was sent. If not, then change the whitelist entry to match what's shown in the return path header.
Yes, I have an opinion.
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