The first recommendation is to remove the channel(s), reboot the Roku (dot NOT skip this step), and then install the channel again. Most times that resolves the problem. If it doesn't, then come back and give us an update.
Dan
Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.