Sorry,
Read question wrong

It looks to me as though a family member who has access to editing your tree on
Tribalpages has possibly done it or even passed on the password as I think from memory you can do that on Tribalpages

This would not necessarily be any of the names you found with a tree on Ancestry.
Worth asking the people you have allowed access
EDIT.......it seems it would have been edited on T/Pages

Something which happened to me years ago on Anc was my tree was visible and I was able to edit etc.
However, one day after not using it for a while, I found I couldn't access my own
tree 
My password was the same for all 3 which I had on Anc yet I couldn't access this
one.
I sent a few messages through the (get in touch with the owner) button asking who this was that had access to my tree etc. and hoping the messages would come back to my own email as I owned the tree & had no email nor a reply from the "ghost"
I then sent Anc a message with my query, explaining what had happened.
To this day I don't know what Anc did, if anything but that tree is no longer on Anc

Strange but true

Annie