There’s a bug where if you have a pending notification and try to summon the herald, the sticky will disappear but the herald won’t come. But since the timers keep running in the background, she will eventually appear.
I’m investigating why it doesn’t come in your case. On a new savefile, making the inventory full is not enough to make the bug happen, so maybe there’s something else involved.
I had reproduced this bug in the past by having a pending shop notification in the notification list.