Hi @jshap
Thanks for contacting Auth0 Community.
You can review this community post to understand auto-login post signup https://community.auth0.com/t/is-there-a-way-to-disable-auto-login-right-after-signup/70258
Regarding the error you are seeing there is likely some erroneous condition in your setup, please review this post for some pointers https://community.auth0.com/t/error-unable-to-issue-redirect-for-oauth-2-0-transaction/108012
These may also help you:
https://community.auth0.com/t/unable-to-issue-redirect-for-oauth-2-0-transaction-login/100560/3
Warm regards.