So I had the same problem as you with the same versions of UE4 and Wwise. I even tested other versions of both Ue4 and Wwise, the problem still persisted.
After a lot of research, I discovered that it's a UE4 issue, that started around 4.15. Whenever you add a third party plugin as a project plugin, hot reload will just stop working, and you'll have to rebuild your project, every time you change the C++ code.
So to fix this, what we did is, we made Wwise as a Engine plugin, rather than a project specific plugin. If you dontknow what s the difference, here's a link. Delete Wwise plugin from your project and make it an engine plugin, and it will work for you, because, an engine plugin, is built just once, so It wont interfere with the hot reload.