I had what appears to be the same issue with two channels on my Ultra, which appeared sometime after it was updated to software version 13.0 about a week ago. The channels are still there, and are identified if I move to them, but the icon for them is a "blank" placeholder as seen in your image.
The only way I have found, thus far, to restore the icon is to remove the app and and reinstall it, using the * (star) button on the remote. I have not tried a lot of other options, however. I did find that checking for updates to the app (also with the * button). Others have reported that this may fix one, only to have another channel loose its icon later.
Reinstalling the app will add it to the bottom of the menu and you need to move it if you want it back where it was before, so take note of the position before you remove it. For this reason, you probably don't want to remove several at once. One at a time will likely be less trouble. Since you appear to have a lot of them blanked out, you may want to try waiting and see if it self resolves, or just reinstall the ones you really want right now.
EDIT: I just read in another thread that Roku recommends restarting the Roku TV system. Navigate to Settings > System > Power > System restart (on some devices there is no Power option, System restart is just under the System menu). (This is NOT a System of factory reset, which apparently does not fix it!) Note that some people had to do this restart more than once, but on my older Streaming Stick 3 tries still did not fix the only icon that was missing.
