FYI to community members, please be aware and read the response we got from SAP Support:
For your information the AutoSuggest/AutoComplete features have been disabled for higher releases. It was not expected to work as usual. This is due to design changes in WD java and technical limitations. There is a note actually which discusses this. You are requested to kindly follow the note 1760145 which discusses this and a possible workaround.
While the help file still documents these features, it seems that they are not relevant anymore. I would request SAP to update the helpfile and warn developers.
Enabling AutoComplete for InputFields - Developing Java Web Dynpro Applications - SAP Library