Close the screen and open it again, or restart your iPhone. If an app is still blank after that, remove it from the block, folder or limit and add it again.
Steps
Close the screen and open it again. Icons often show up on the second try.
Restart your iPhone.
If an app is still blank, edit the Quick Block, Focus Session, folder or App Limit it's in. Remove the blank app, then add it again.
If you deleted and reinstalled that app, or moved to a new iPhone, pick it again. Your old choice doesn't carry over.
On the block screen you might see "this app" instead of the app's name. It's the same issue: iPhone didn't give us the name in time. The block itself still works.
If blocking isn't working either, see Blocking isn't working: start here.
Why this happens
To protect your privacy, Apple never tells Slow Time Club which apps you picked. We get a sealed code for each one, and iPhone draws the name and icon on screen for us. Sometimes it draws them late or leaves them blank. After an app update or reinstall, iPhone may also fail to match an old code to the app. We can't fill in the gaps ourselves, because we really don't know which apps they are. Sorry for the confusion.
Related: Why does Slow Time Club need Screen Time access, and is it private? · Moving to a new iPhone
Still stuck? Contact us from Profile → Help and Legal → Contact support and include your User ID (Help and Legal → User ID).