On every drone you have a mass budget. Every time a new component is added, that components weight as well as the weight any required new wiring and mounting hardware get added to the total system mass, and subtracted from the mass budget.
The most recent changes to the Electronics chamber added a lot of mass to the system. No one thing added a lot of mass, but there were a lot of little additions. Enough that we needed to find ways to drop overall mass to meet get back on budget. As part of that round of changes the base plate was made buoyancy neutral.
The side chambers, which ironically were added to be able to add weight to the system, now print with an air pocket. The pocket can be seen in the middle cutaway picture in the figure above. There are still small chambers for adding trim weights, but the new plate design is buoyancy neutral prior to weights being added. As the electronics are merged, going from multiple boards to a single custom board, a single revision of the size ratio of the base plate’s float and weight chambers will provide an easy way to keep the design target buoyancy constant through system mass fluctuation.