Lateral Hire: Simple email read over 100 times in 1 day? Red Flag?

Received a lateral analyst offer a couple of weeks ago from a big bank and HR yesterday reached out to inform me that I’ve passed the background check and inquired whether I would be able to start the new job in 2 weeks. I had sent out an email responding to the HR that I would be able to start in 2 weeks and that I was excited to join the team.

The HR didn’t reply to my email but, over the course of the day, that one simple email that I sent to HR was read over 100+ times (I have an email tracker installed by default which is usually pretty accurate) presumably by a few different people in the company. 

I’ve haven’t come across a situation where a simple email that I sent was reviewed that many times and was wondering if I should be concerned about this and what’s the likely reason for the email being reviewed over 100 times in 1 days. The HR also hasn’t responded to my email as well if that matters. 

Maybe I'm a bit pessimistic but when relatively unusual things like this occur, I have a tendency to feel like the team may screw me over (e.g., rescind offer, hire me and then fire me within a few months, interview others even though I accepted offer already, etc) and the last thing that I want in this type of economy is to move into an unstable job/company and get screwed over somehow. 

Thanks in advance.