As I had that issue twice already and forgot the solution, I write it down here now 🙂
The issue is, that a search operation in Filenet Admin Console (ACCE) hangs if your browser language is set to a non-english language. Just set English as the default browser language and everything works again.
In SystemOut.log you see a message like that:
ERROR [WebContainer : 7] - method name: determineBadClassRetry principal name: P8AdminT Global Transaction: false User Transaction: false Exception Info: Class "" not found. com.filenet.api.exception.EngineRuntimeException: FNRCE0002E: E_BAD_CLASSID: Class "" not found.
This issue is already documented in that technote: