Ensure that the trays are positioned correctly inside the bento box.
The trays should sit flat at the bottom and is designed to fit on top without forcing it.
Check that the trays are aligned with the edges and that nothing is obstructing them. Gently pressing them into place usually ensures a secure fit.
If your bento outer shell was purchased before 2022 and uses the patterned trays, the current clear trays and silicone lid inserts will not be compatible, as the design specifications have changed. Older bentos can only be used with the original trays and inserts they were designed for.