Play Polypanels are more robust than the standard panels but the connections are looser. It's the perfect combination for young ones or anyone who doesn't want to deal with the full power of the mighty polypanel!
That said, printer calibration can still affect the connection strength of your Polypanels, making them hard to connect or to loose to hold together. The first thing you might want to play around with is extrusion multiplier or flow rate. More troubleshooting tips on the Polypanels webpage.
*07/09/18 Edit* Minor fix (one edge wasn't correctly rounded)