Lead creation via the SOAP API appears to take some time to actually create the lead and have it visible, but I can't seem to find any documentation on what this delay might be and if it exists in the REST API also.
Can anyone help me figure out why this delay is happening?
There is often a delay from Forms or API depending on the volume of leads and processing your instance is doing. It can take 10 mins sometimes.
If it goes beyond this, you may want to troubleshoot on both ends and call support.