Hello Julia,
We did actually also have this issue recently, which we think is down to a change in 3d printing technology used to manufacture the lids.
We solved it by putting O-rings on the underside of the lids. This is the part we are using:
https://uk.rs-online.com/web/p/gaskets-o-rings/1965666
But anything similar should work. Important quantities are the internal diameter (external can be a little different and still fine), and material (such that it is autoclavable).
We found that putting these in our lids and screwing them down tight fixed the issues.
Harrison