When river set to take elevations from terrain and underlying terrain changes height, river device does not update and river stays in previous height. You need to manualy change to different setting and back, so device will take in account changes:
I don’t think this is a bug, it’s not just a feature, as I can’t remember the river device behaving differently in older version. I do think it is an important feature WM is missing out on, it would be really sweet to have an option to let it auto update to alterations in the terrain, though I also understand why someone woulnd’t want this, as it can lead to unpredictable results.
I can manualy update all rivers, but this is quite tedious in case you have 20 rivers in device and with each terrain update you have to do it again. So there should be button “update all”, or just do it automaticaly during build phase. I had to countless time rebuild just because I forget to update rivers again, or I just didnt notice, that my change modified height of terrain by 1-2 meters, so I had to rebuild again…
It is a feature, in that it holding the river geometry constant when no editing is performed seems like it would be the least-surprising result rather than having the rivers potentially bounce up or down due to differences in the input when building at different resolutions, etc.
You should be able to set all of the rivers to the terrain at once using the button on the river editor panel. I’ve cleaned this up a bit for the next version to make it more clear.