Citrix receiver IOS client on ipad

You need to turn up APM debug log and see what is happening when iOS client is trying to authenticate - where does it get stuck. You can also turn up VDI debug log via tmsh in addition to overall APM debug log:

tmsh modify sys db log.vdi.level value debug tmsh modify sys db log.accesscontrol.level value debug

Don't forget to set them both to notice after you're done debugging