found it, this error appears when the target you want to look at is exactly alligned with the "up" vector. eg:

```
var target=Vector3(0,10,0)
var tform=Transform.IDENTITY
print(tfrom.looking_at(target, Vector3(0,1,0))
```

this happens because *The transform will first be rotated around the given up vector, and then fully aligned to the target by a further rotation around an axis perpendicular to both the target and up vectors.*

but if the up vector is already perfectly alligned with the target, it cannot find the perpendicular axis for the second step.

Not a real error tbh