I made my own firmware (1.21.0) with frozen module (just folder frozened with package("utils", base_path="/project/frozen")) named 'utils' with some py-files.
It works ok until i not upload new file 'newfile.py' that was not frozened, to folder 'utils'. Like 'utils/newfile.py'
After this, the files in the frozen module become inaccessible: ImportError: no module named 'utils.oldfile'
Only new file 'newfile.py' is accessible.

Even if i delete all the files from this folder, but leave the folder to exist, they remain inaccessible.
If i delete the folder with the name of the frozen module, then everything returns to its place.

I think this is bad behavior. I think new files should coexist and work together with frozen ones. Until I write a file with the exact same name of an already frozen file in this module into this folder. Just like overwriting a file.
In other words, now if i create folder with name of forzened module, i turn off the frozened module with this name.