Just got ATSC 3.0 signals here on Monday. I have Channels (beta) running on 3 ATV's. I am seeing that changing channels between the 3.0 signals is very slow. Understood HEVC takes longer to build the stream. BUT I also have HDHomerun apps installed on the ATV's, and on the LG OLED and the OLED also has a built in IPTV app of its own. Changing 3.0 stations on HDHomerun or the built in app is much much faster than on Channels. On Channels, video stabilizes after 6 seconds, audio after 8 seconds.
Also another possible bug, When watching 3.0 feeds the audio sample rate is reporting at 46034hz. The chief engineer at the station reports they are encoding at 48000hz which is the standard. Not sure if the decoder is malfunctioning or stats is just improperly reporting the sample rate.