Facebook: Difference between 'last active' and 'on mobile' status.?

[Aurora]

Hey, I'm really hoping someone can help me out here. I've researched but can't find anything.
I was talking to a friend a few days ago via mobile web (iPhone). I was chatting via the Facebook app. She also has an iPhone-I don't know if she has messenger too, but she def has the Facebook app.

Usually when we message it says 'active now' if she is online and 'active x minutes ago' if she's not.
Now, it's changed and has been like this for a couple of says.
Instead of saying 'active x minutes ago' it just says 'on mobile'.

I would like to know why this is.
I thought it may be due to her being inactive on Facebook for, for example, more than 24hrs, as I recall seeing such time stamps for other people that say things like 'active 19hrs ago' but never a 24hr+ one. Which made me think maybe Facebook changes the status to 'on mobile' afterr more than 24hrs. But just speculating.

Any ideas?

[Rebeccat]

Facebook seems to have gotten rid of this in the last 24 hours. Before it was saying 'active now' for when people were online on their computers or their mobile app. Now it will only say 'active now' if she is actually on her mobile app at that exact time and if you are friends with her.

If she is on her computer messaging you it won't say active now or active x mins ago it will be blank or say 'on mobile'. Also note you have to be friends with her to see this.
It's incredibly annoying and i want them to change it back, if you figure out a way let me know please