for the dip to black issue, and if you are always playing back on more than 1 server , i always use manual preroll set it to 3 seconds , try connect the 2 videos together but in 2 different layers with manual preroll , plus test the playback on the output screen not the production, sometimes the preview is not as smooth as the server main output.
for the 60 hz issue , currently in the market everyone advertise they are 60 hz but in reality they are mostly 59.94 , so to get a solid 60 hz sync while you have so many components together is hard and troublesome what u did to fix it in-fact is what i always do