Concurrent workflow instances limited at ~120 instead of 4500

So I was observing workflows dashboard this morning, because I made a quite significant changes to my worker last night. I was expecting approximately 400 instances per minute that are spawned from a parent workflow that are batched into 4 groups, 100 per 15 seconds. I was expecting all to be ran on their given interval. But instead of all been completed, I see a huge number of workflow instances being queued; then it accumulated at least 1 thousand of instances. I observed it on time, and turned off the scheduler 'cron'. Hence stopping the ability to generate more queued instances. I am not sure if there is anything from worker that is limiting the ability from achieving the ideal concurrent instances, or any other reason, please help Also the workflow dashboard also been extremly slow. And whenever I push any new debugging changes, it failed the build [ERROR] A request to the Cloudflare API (/accounts/[account_id]/workflows/set-etf-profiles-workflow) failed. 10:38:31.885
10:38:31.885 workflows.api.error.internal_server [code: 10001] 10:38:31.885
10:38:31.885 If you think this is a bug, please open an issue at: https://github.com/cloudflare/workers-sdk/issues/new/choose

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