Also, in the tutorial, when he first adds the flat tank it is already full with particles. But when I add it, it's empty and it takes a series of frames for it to form a wave.
I guess the flat tank functionality has changed or I'm doing something wrong?
To fix it, you can either uncheck “Kill inside Collision” on the “wavetank” (Ocean Source).
Or, make the “wavetank” editable (right click “allow editing of content”), dive inside, find “collision_sdf”, and on the the Voxel Size param delete the channel and set a value manually (eg 0.2).
I would recommend setting the grid scale to 2 in the Ocean Source parameters window. This should fix your problem for the time being. We will fix it on our end for future builds.