Measurements with multimeter giving paradoxical values
The answer is in the question.


  There was a resistor that was not soldered properly, so the point was
  floating (as in not connected to anything). After connecting it, the
  multimeter gave expected values.


For a voltmeter to work, there needs to be a current through a large resistor, typically 1M on lower end meters. Since one side of the meter was floating, it was an open circuit, therefore no current flow. Probe any point on your board and leave one probe in the air. The same thing will happen. Nothing magical or paradoxical here...