Following the notes at step 9 of the install guide we have been hosting Experience Builder at a subdirectory behind our proxy. https://developers.arcgis.com/experience-builder/guide/install-guide/
In v1.13 this appears to be broken - login no longer works (stuck at the page subdirectory/page/set-portalurl with the ExB loading icon but no form).
The following error is thrown:
index.js:1 Error: Should signIn
at QS.failedToInitSession (index.js:2:483193)
at QS.<anonymous> (index.js:2:483026)
at Generator.next (<anonymous>)
at a (index.js:2:478493)