I created a new timeline, added an entry...and it doesn't show up.

The timeline is here - https://www.worldanvil.com/w/parhelion-drykos/t2/history-of-parhelion---1585-part-two-timeline - and the timeline entry is here - https://www.worldanvil.com/w/parhelion-drykos/h/e1ea4d53-44c5-4c98-af44-37c5714a7a99 - and it should be noted the timeline is connected to the right timeline, it just doesn't appear on the timeline itself.

Interestingly, when I revert it to an older style timeline it does work correctly. I'll do so in a few days as a temporary fix so my players can use it.

Make a new timeline and add a new entry, I assume. This is the second time I've made this timeline and it has done the same thing.