I ran into the stuck 166 as well. I was running a London-Reigate service and got a perpetual red signal leaving Redhill. I noticed the 166 bound for Gatwick was sitting with doors open despite a green signal (and had been for quite a while per the departure board.) I took over the 166 service, moved it past the green signal, stopped, got back in my 377 and the 166 then continued on its way and I was able to complete the service. Not ideal obviously. Playing on Series X fwiw.