Hi Michał,
If test = prod, than no functionalities should be lost, although if there are differences, then this might happen.
Some examples (I'm assuming here full export import - all processes, presentation etc. in application):
2023-11-01 - we make our first deploy TEST -> PROD
2023-11-07 - there is a bug, which is fixed on PROD only
2023-11-08 - we move PROD -> TEST, and TEST -> PROD
No functionalities should be lost.
2023-11-01 - we make our first deploy TEST -> PROD
2023-11-05 - we started creating new functionalities on TEST
2023-11-07 - there is a bug, which is fixed on PROD only
2023-11-08 - we move PROD -> TEST, and TEST -> PROD
Functionalities/changes introduced on 2023-11-05 will be lost.
Basically any quick/hot fixes, should be done manually on each environment, or if it's possible - do them with import/export, but in most cases you can't because there is already some new unfinished feature on DEV/TEST and you want to apply only that one specific hotfix, and not those unfinished features.
Beneath import/export mechanism there are GUID's - each item you configure inside Designer Studio gets GUID - that's like ID, but it's equal on all environments.
What import does is that it drops (or marks as deleted) all the configurations which GUID's are not in the app package, updates those, which changed, and appends new ones.
Above is based on my experience, I can't guarantee that's exact implementation though - if anyone have different experiences, I'll be glad to update my knowledge :)