This description sounds awfully like a clearing board:
If this is the case, it’s been applied incorrectly. The above device only allow bees out in one direction and discourages them back in, which could explain your problem. Clearing boards aren’t typically required for flowhives.
Check out this video, at about 1:50 min mark, Cedar makes the necessary adjustments to ensure the extraction side of the flow frames sit flush with each other and remove any gaps that may enable the bees to escape:
Welcome to the forum @Val