On the publish server, are you able to reproduce the issue, when you bypass the dispatcher(i.e., access the publish server using its host & port directly)?
a) If not, then enable DEBUG logging for dispatcher, and see which filter is blocking the request. You can then allow this request to go through dispatcher.
b) If it's still reproducible, invalidate cache & rebuild clientlibs via File System, as per [1], clear all browser cache & cookies, close all browser tabs & windows, open a new one in Incognito mode, and then verify whether the issue is still reproducible.
Hope it helps !!
[1] https://helpx.adobe.com/experience-manager/kb/How-to-force-a-recompilation-of-all-Sling-scripts-jsps...