Conversation view groups messages from the same conversation together in your Inbox, so they are easy to follow and respond to. This article explains how to disable this feature.
How does conversation view work?
ProtonMail cannot read the contents of emails because all messages are stored using zero-access encryption. We therefore use advanced heuristics on the email headers, subject line, and conversation participants to match and thread messages.
This does leave a small amount of room for error, however, particularly if some of these elements are missing (for example, not all email providers include all the standard information in their email headers).
How to disable conversation view
If you prefer to disable this feature, simply log in to mail.protonmail.com, go to Settings → Appearance → Other and turn Conversation grouping off.