it’s only letting me schedule one blog post at a time

That’s a crappy summary, but I’m not sure how to make it shorter?

What’s happening: I wrote a blog post & scheduled it to go live next Tuesday. So far, so good.

I wrote another one, scheduled it to go live next Wednesday, saved it, & when I went to look at my scheduled posts, it was the only one on the list. The post I did first had disappeared.

I rewrote the first one — with the second one still open in a separate tab — & saved it. That one showed up on the list of scheduled posts, & the second one was gone.

So now I’ve got each post open in its own tab. I save one, & the other disappears.

I updated plugins. Still happening.

I deactivated all my plugins, so I could play the ‘which plugin is causing the problem & what can I replace it with’ game, but the same thing happens, even with all my plugins deactivated.

I reactivated them all, reinstalled the latest wordpress. Still happening.

I tried saving the second one as a draft, figuring I could at least have it saved & schedule it later, or post it by hand the day it’s due to go up, but that draft post replaced the other scheduled post.

Apparently I can only have one draft or scheduled post saved at a time.

I’m running WP 5.6.2. Please let me know what other information might be useful, & please, please help me figure this out!

Many thanks!

The page I need help with: [log in to see the link]