Emails not sending when requesting signatures for DocuSign API

I have written the following two methods for sending requests for signatures.

From template: https://github.com/wadewegner/docusign-sample/blob/master/src/DocuSign/DocuSignClient.cs#L215

From binary: https://github.com/wadewegner/docusign-sample/blob/master/src/DocuSign/DocuSignClient.cs#L152

Both work great and I can see they are out for signature:

The trouble is receiving the email requesting the signature is spotty at best. Early on in my testing it seemed I'd (mostly) get the email, but a couple days in and I haven't received any of the emails you see in the image above.

I'm using a developer sandbox. Is there some kind of restriction?

Also, it seems sending to a different email address from the one I registered is particularly problematic. Are there even more restrictions?

Thank you!

Edit: adding additional info requested.

REQUEST #1 (posting document):

POST https://demo.docusign.net/restapi/v2/accounts/892965/envelopes HTTP/1.1
X-DocuSign-Authentication: <DocuSignCredentials>...</DocuSignCredentials>
Accept: application/json
Content-Type: multipart/form-data; boundary="BOUNDARY"
Host: demo.docusign.net
Content-Length: 91206
Expect: 100-continue

--BOUNDARY
Content-Type: application/xml; charset=utf-8
Content-Disposition: form-data

<envelopeDefinition xmlns="http://www.docusign.com/restapi"><emailSubject>DocuSign API - Signature Request on Document</emailSubject><status>sent</status><documents><document><documentId>1</documentId><name>test.pdf</name></document></documents><recipients><signers><signer><recipientId>1</recipientId><email>wade.wegner@gmail.com</email><name>Wade Wegner</name><tabs><signHereTabs><signHere><xPosition>100</xPosition><yPosition>100</yPosition><documentId>1</documentId><pageNumber>1</pageNumber></signHere></signHereTabs></tabs></signer></signers></recipients></envelopeDefinition>
--BOUNDARY
Content-Disposition: form-data; name=test; filename=test.pdf; filename*=utf-8''test.pdf

<truncating binary>

REQUEST #2 (from template):

POST https://demo.docusign.net/restapi/v2/accounts/892965/envelopes HTTP/1.1
X-DocuSign-Authentication: <DocuSignCredentials>...</DocuSignCredentials>
Accept: application/json
Content-Type: application/xml; charset=utf-8
Host: demo.docusign.net
Content-Length: 421
Expect: 100-continue

<envelopeDefinition xmlns="http://www.docusign.com/restapi"><status>sent</status><emailSubject>DocuSign API - Signature Request from Template</emailSubject><templateId>29CB97E5-DCE1-4C14-91A8-A8317BCD29AD</templateId><templateRoles><templateRole><name>Wade Wegner</name><email>wade.wegner@gmail.com</email><roleName>Signing Role</roleName><clientUserId>1</clientUserId></templateRole></templateRoles></envelopeDefinition>

The ClientUserId causes a recipient to be an embedded recipient. If you provide a value then DocuSign will not send emails. The expectation is that you are going to handle the communication with the signer. This allows you to embed the signing experience within your own website or application.