This is most noticeable if you work on creating a large assembly and are constantly switching between editing sub-parts, as the design evolves, in a single Alibre session. i.e. over the course of a working day.
This has been previously discussed and shown (you can see the memory increasing each time you open a workspace, but it never fully gets released when you close one) in the first post of a thread I started on UI performance ...
https://www.alibre.com/forum/index.php?threads/v25-some-aspects-of-ui-performance-are-visibly-not-as-good-as-v24.23552/
It's not new to v25, this has been the case for quite sometime. If you don't have much RAM in your machine, you notice it more as the OS starts using the disc swap file and that manifests itself as the application becoming more and more sluggish. Short term I improved it by adding more RAM (from 8GB to 32GB).
Doesn't solve the underlying issue though, although I do believe that Alibre are constantly working on performance improvements, hopefully addressing this one soon is one of them!