Hello there @UberPz!
Checking with my peers, there are a few possible cultrips for this issue. It’s possibe that during the bake, the ShallowWaterRiver component failed to register properly. You can force an update by moving the actor slightly from its position, then setting it back. You can also re-addor re-create the actor. Or you can reset it by selecting the element in Outliner, searching the Details panel, and hitting the Reset option.
If the issue, then I would suggest reviewing the workflow used to setup your river. For further reading, there’s a similar scenario in the thread below, along with docs and guides from the community. Please check them out: