This is very common with brushes that are sold around the world, most brushes are ordered from china and are shipped in a container that is placed on a boat. The boat travels for 30 days to get to Canada, during its voyage the container gets really hot and the glue in the Ferrule melts. The melted glue usually ends up on one side of the brush and loosens the feral from the handle. There is no way to avoid this, this usually happens to about 5% of the brushes. but there is a quick fix.
You can take a hairdryer and heat up the bottom of the Ferrule this will melt the glue again, once you see that its a little shiny you can insert the handle back into the Ferrule. Heating up the bottom of the Ferrule usually takes no more than 30seconds.
Your second option is to send the brushes back to us and we can correct the problem for you.
Hopefully this helped you.
Thank you