The problem occurs because there are 2 conditions that need to be fulfilled.
Its programmed to spin at set RPM for 6 mins.
Before it can initiate a full speed spin it needs to ensure the drum is balanced. If its off balanced it will damage the spin motor and other parts of the machine in short order. (reference old machines that sound like an earthquake during spin cycles). It will keep attempting to adjust the clothes by start-stopping so clothes can fall in place. Only when the vibrations are down to acceptable levels will the machine initiate a full speed spin dry. Machine will stay stuck at set spin time until condition 2 is fulfilled.
The way to fix this is to open up the machine, untangle balled up clothes and allow the spin dry to resume.