When you open a reply that someone sent you, Mailtrack may sometimes register this as an "open" from that recipient, even though you were the one viewing the message. This can make it look like the recipient opened the email multiple times when in fact you were the one reading it.
Mailtrack has a mechanism that can detect when you open a sent email yourself, and ignore that open, but this only works if you are viewing the email on a computer browser that has the Mailtrack browser extension installed or on the Mailtrack app for Android and iOS. If you open the reply on a different device, browser, or Google account that does not have the extension installed, Mailtrack has no way to recognize that it's you opening it, so the open can be mistakenly attributed to the recipient.
This issue can occur in particular when opening sent emails on a mobile phone. If you use the Gmail app on mobile to open sent emails, false opens are more likely to be recorded. Using the Mailtrack app instead prevents false opens, so if you are a mobile user who cannot use the desktop browser extension, installing the Mailtrack app is a recommended alternative.
To avoid this, make sure you open sent mails and replies using a browser where the Mailtrack extension is installed and active or the Mailtrack app.