Hart and Mason family shared DNA

Over the last few days, FamilyTreeDNA has been showing a few new matches in my results.
Many of those are quite small matches, so would be very distant cousins but one, in particular, showed a range of 2nd - 4th cousin with 87 shared centimorgans, the longest block being 29.
This was amongst my highest matches so I felt it would be fairly significant.
I sent an email and received a reply from Jen who said she had done the test mainly out of curiosity about her ethnic origins and that she knew very little about family history research, so didn't feel she could offer much help as to where we connected.

I explained we could be 3rd cousins and asked if she could let me know any of her family surnames.

She replied with 5 surnames, 2 of them being JACKSON and BELL.
I went to my family tree program and Bingo!
I found that a maternal great-grand-aunt, Rose May HART had married John Thomas BELL in 1913.

Rose May HART, born in 1889 at Echuca, Victoria, was a younger sister of my great grandmother, Margaret FLEMING nee HART.  They were daughters of Agnes nee MASON and Peter HART.

John, known as Jack, and Rose had 2 children.  Amelia Agnes BELL born 1914 at Wangaratta and John Desmond BELL born in 1921 at Wangaratta.

Amelia Agnes BELL had married Charles JACKSON and they were Jen's paternal grandparents!
Sadly Amelia had died in childbirth so her son never knew her but Jen says he remembers the HART surname.

I look forward to meeting Jen and her Dad sometime later this year.

FTDNA's "In common with" tool and chromosome browser produced 2 other matches on the same chromosome as Jen although probably further back. (I have privatised the results in the screenshot below)

The 2 other matches are American and on contact with their kit administrator, I was told their ancestors had all been in the United States since the 1800s.

A bit of a mystery somewhere it seems.