Reported internally by @olegbl:

As far as I can tell, the calculation inside Point.isBefore is not quite right when comparing an Element Point to a Text Point:

if ($isElementNode(aNode)) {
  const aNodeDescendant = aNode.getDescendantByIndex(aOffset);
  aNode = aNodeDescendant != null ? aNodeDescendant : aNode;
}

changes the value of aNode but does not change aOffset.
As a result, when it gets used down below in

if (aNode === bNode) {
  return aOffset < bOffset;
}

The aOffset is being applied twice and leads to an incorrect result.
e.g.:

// nodes
1 (element node)
  2 (text node)
  3 (element node)
    4 (text node)
    5 (text node)
                  <-- point1 is here
    6 (text node) <-- point2 is inside here
  7 (text node)

// point1
key = 3
offset = 2

// point2
key = 6
offset = 1

// test:
point1.isBefore(point2) // this should be true

// aNode = node 3
// aOffset = 2
// bNode = node 6
// bOffset = 1

if ($isElementNode(aNode)) {
  const aNodeDescendant = aNode.getDescendantByIndex(aOffset);
  aNode = aNodeDescendant != null ? aNodeDescendant : aNode;
}

// aNode = node 6

if (aNode === bNode) { // true
  return aOffset < bOffset; // 2 < 1 = false (this is wrong)
}