Small soul core not activating Stone altar

Have a Small Soul Core, trying to activate a Stone Altar, but it just says I need a Small Soul Core

I had the same issue last night. I didn't talk to Alva, found the key and couldn't use it. It worked in a new instance when I talked with Alva first.

Also experiencing the same currently.
Here's a vid:
https://streamable.com/8tpww9

Same here for the first alter - cruel difficulty. Created new instance, and it worked.

Bug Report ID: #1783645406

Same here, altar in upper right corner of map with access to treasure room. Altar, partially covered by checkpoint.

UPDATE:
Appears to be by design. All treasure room altars are not accessible after first play through.