Anyone tested with AMD card and is it running fine with dynamic lights on viewport?
Maybe reproducible by 1: creating new project 2: New map with some assets 3: set light to dynamic 4: set Num dynamic shadow cascades to 4 5: it should start to slow down like weird shuttering.
R9 270, last year it functioned much better even when dynamic shadows quality was set to 4. If anyone has AMD cards please try this scenario.