Recreated, seems to be the way resolume captures the alpha ? Switching alpha type on receiver end has no effect in 7.1, using blend mode add set to 50% or "50 add" set to full take away the artifacts with this setup.
PC 1 : 2 layers, layer 1 text animator with random y position really fast, layer 2 bypassed with solid red, NDI composition output on, layer 2 routed to a slice in advanced output for NDI output
PC 2 : Arena 2 layers, layer 1 NDI "screen 1" red color source, layer 2 NDI composition source
NDI Studio monitor, source is "screen 1", set overlay to use alpha and pick "composition" for your overlay
