For anyone who is a fan of gem blocks, you will know that there is no way for acrylic gems to adhere to wood without an adhesive. Each brand meets these challenges differently. TimberPlay uses durable tape as the adhesive. This ensures that gems remain intact (some types of glue can damage the backing of the gems) but also results in a little gem wobble; in other words, the gems have a cushion beneath them and may move against that cushion. If they fall out, you just stick them back.
Whatever adhesive is used (e.g., tape, wood glue, or superglue), it is not uncommon for gems to come off during transport but also through play. This is why there is a choking warning on gem blocks--because of the possibility that a child comes into contact with the gem.