Just a quick update: The issue wasn’t due to multiple Midjourney submissions clogging the scenario; it was actually my User API that had expired, and I later realized I’d run out of operations.
If you need to check your remaining operations on User API, go to the Discord Accounts section. Under the Plan column, you’ll see a number indicating your remaining operations—if it shows 0, it means you’re out, even if the status is marked as active.
For your information, I’m now able to send multiple /imagine requests to Midjourney without any issues.