Is there a way to refresh the cache in Umbraco for the Content Delivery API. I'm seeing items in the backoffice, however, when I get all the content from the Content Delivery API it's clearly missing items.

Try switch to v1 i had the same issue yesterday and switching from v2 to v1 solved it

We're seeing in V1 as well.

Is this a known issue?

Not that I could find. The only relevant Github issue I found was regarding the item count was including items in the recycle bin. Also, this issue is a pain because we can't reliably reproduce it.

It might be a good idea to open a new GitHub issue to assist the Umbraco team, considering that the Content Delivery API is still in its early stages, but in my opinion its a great idea. If you provide a link to the GitHub issue here, I will add the issues I've encountered, which should help them address the problems more effectively.

I'm planning on trying to reproduce the error then open up a ticket.