On a fresh install, both Twitter and X share links are inserted in the core_share_links table.
This happens because the file \applications\core\data\schema.json was updated in 4.7.14 to insert a new row (ID 10), but the old one (ID 0) was not removed:
"inserts": {
"0": {
"share_id": 1,
"share_title": "Twitter",
"share_key": "twitter",
"share_enabled": 1,
"share_position": 1,
"share_groups": "*"
},
[...]
"10": {
"share_id": "13",
"share_title": "X",
"share_key": "x",
"share_enabled": "1",
"share_position": "13",
"share_canonical": "1",
"share_groups": "*",
"share_autoshare": "0"
}
},