Milk kefir tubers usually survive the transport quite well.
The white liquid is a nutrient solution and provides the small tubers with all the important nutrients during their journey and the stay until they are used. They can easily stay in the bag for a long time. If the bag is distended, this indicates metabolism, not spoilage!
Just put it on and look at it again after 1 day. Is the drink cloudy? Is it bubbling? Does it taste more sour and less sweet? Then everything is good!