Exclamation S Planner not showing up custom calendar

Hi there. I'm a subscriber of a few sports custom calendars on Google that show up nicely on Google Calendar and on S Planner, except for one! It used to show up properly, but now it doesn't (which means I don't really know when it stopped). I subscribe to the League, Cup, Continental and State championship calendars for my team, and only the National League one doesn't show up on the phone. All the others show up nicely.

The box on S Planner to show that calendar is ticked, just like every other. I have tried unsubscribing from it on Google Calendar and then re-subscribing, changing its colors... but nothing made it show up on the phone.

Anyone has any suggestions?

Thanks!