I am in the Opening Ceremonies event if this has anything to do with this bug.
My opponent attacked with 3 monsters, one of which being a proc'd Reflective Golem, I blocked and destroyed them all. On my opponent's main phase 2 they placed another reflective golem and we just sat while the timer said it was still my opponent's turn. When their timer finally ran out, somehow, they were back on main phase 1, dropped another monster and attacked with the reflective golem in what appeared to be one long turn with 2 battle phases