Timeline dissapeard for a projected connected to SharePoint List

Hello,

I have a project that I connected to a SharePoint list. I had a timeline, but the last time I opened it, the timeline was blank, and I can't add anything to it. It only shows up as a blank space.

Does anyone know a fix for this without having to create a new SharePoint list?

Before

Now

(Note: If you hover the mouse above it, you can see that there are activities in the timeline.)