Okay, finally got the original nrf24l01 SMD modules with the square chip visible... As exptected, things work just fine now, so the culprit of my issues was really the incompatible/fake "nrf24l01" SMD modules with the epoxy blob. If you want to use normal nrf24l01+ modules together with this smd gateway, DO
NOT USE the smd module with the epoxy blob, as they won't work.
Using only the fake SMD modules might work, too, but mixing the fake modules with real ones does not work.