mailpoet stats different from sendgrid stats

Hi,

I am using mailpoet in one of my sites for the last 3 years. A few weeks ago I set it up to work with sendgrid as you suggested.
It is working fine.
I have noticed that the stats in my sendgrid account are very different from the stats in my mailpoet dashboard.
Example: for my last newsletter, I sent out 165 mails. According to sendgrid 107 were opened, according to mailpoet only 79.
The previous letter , I sent 159 mails. According to sendgrid 143 were opened and according to mailpoet only 90.

Can you tell me why these stats are not the same. Can you fix this.
I feel at the moment the stats in mailpoet are not reliable.

Thanks,

https://www.ads-software.com/plugins/wysija-newsletters/