Why is a "seen time" on web in messages different from the "seen time" in..?

Hello,
I've announced, that my ex, which I am trying to get back has read my message in certain time in the morning. That time was initially the same in both (on web and on the FB mobile app). But later I've announced that time has changed two times on mobile app. It remains the same on web. Can somebody explain?

Thank you

 

It's hard to say and I'm betting almost nobody will know exactly what's happening but Facebook themselves Perhaps web and mobile segments are separated so maybe she viewed your message again in mobile instead of web and that's the time you are seeing on the mobile? Wild guess!

 

Thanks for your answer. I have thought about the same. Does exist some support from facebook, something where they can answer it surely? I think, it could be quite important and it can help me to find out if she is definitely over me or if she is interested and thinking about it..

 

I looked again on the conversation. The both times are the same now, but I am still curious what does it mean...