Hi there,
Honestly, we didn't know why it happened actually. But based on what i have google-ed as listed below, we found out that
1. If you receive a message from, or are about to send a message to, someone whose email service doesn’t support TLS encryption, you’ll see a broken lock icon in the message.
2. If you receive a message that can’t be authenticated, you’ll see a question mark in place of the sender’s profile photo, corporate logo, or avatar.
References:
https://blog.google/products/gmail/making-email-safer-for-you-posted-by/
Please advice.