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I have a known Jewish great great grandmother and on My Heritage get a huge number of Jewish matches. My Heritage is an Israeli company and very popular in those countries hence their (I believe) overrepresentation in my matches.

They are also likely to be overrepresented because they are from an endogamous community, which can make distant matches share more DNA with each other than would be expected for the relationship.

How many segments and how large are the segments shared with the 62.8cM match?

I do find at MyHeritage that for some of my relatives Scandinavian matches pop up sharing around 30cM, but they're over several segments of 6 to 8cM, which aren't very reliable.  But if the segments are larger and the SNP count is quite high then they could be meaningful matches.

The Bishops Transcripts for Axminster (available on Familysearch) around 1800 give the mother's first name and her maiden surname, and the name of her father. 

I wasn't thinking of the ethnicity estimates.  My parent tested at FamilyTreeDNA and uploaded to MyHeritage, so we are able to actually see the segments that we think were inherited from various ancestors (based on shared segments with known cousins).

My other parent shares no DNA at all with a 3C1R - there's absolutely nothing amiss in either lineage though.  The uncle (3C) of the person who doesn't match, is a weak weak.  Yet 4th cousins from this line (going back a generation to siblings of the mutual gtgt-grandmother who was born about 1800) share more DNA than the 3C.  It's just the way things DNA is passed down.  A 5C (descends from the gtgt-grandmother's maternal uncle) popped up on the matchlist recently too.

It's "Modify". It should be next to "Quote".

Thank you.  I only have Quote, but not Modify.