Following up with a recruiter after email was ignored?

Hi everyone,

During one of my coffee chats, I managed to obtain a recruiter's email for a brokerage as they were close to this person. I then proceeded to email the recruiter for an informational interview. Initially, I didn't get a response. Fast forward 1+ month plus later, they responded to my email saying we should get in touch within the next few weeks. I was traveling at the time and had no access to my email, so I wasn't able to reply until 4 days later. The content of my email was your standard "no need to apologize, thanks for getting back to me, here is a list of my available time, etc".

Now I have a tracker on my emails, so I know if/when they have been opened. I was quite surprised to find it showing a notification, saying my email was opened around Sunday evening. Usually, people respond about 10 min - 1 hour after the initial opening, but this time I didn't get any. Since it was the weekend, I assumed I would get it sometime during the following week, but it never came.

Should I follow up? Or was my email purposely ignored? Did they decide to respond over the week after seeing my email on a weekend but got swamped with other things? What do you guys think?