How to find cause of SQL-Server Full-Text Index Auto-Population Error?
Using the Microsoft Error Code Lookup Tool shows Error 0x80070005 is "Access Denied".  This is the output from the tool:

# for hex 0x80070005 / decimal -2147024891 :
  COR_E_UNAUTHORIZEDACCESS                                      corerror.h
# MessageText:
# Access is denied.
  DIERR_OTHERAPPHASPRIO                                         dinput.h
  DIERR_READONLY                                                dinput.h
  DIERR_HANDLEEXISTS                                            dinput.h
  DSERR_ACCESSDENIED                                            dsound.h
  ecAccessDenied                                                ec.h
  ecPropSecurityViolation                                       ec.h
  MAPI_E_NO_ACCESS                                              mapicode.h
  STIERR_READONLY                                               stierr.h
  STIERR_NOTINITIALIZED                                         stierr.h
  E_ACCESSDENIED                                                winerror.h
# General access denied error
# 11 matches found for "0x80070005"

Ensure the service accounts used by SQL Server, SQL Server Agent, and SQL Full-text Filter Daemon Launcher Windows Services have the correct access.  Microsoft Docs has some great details about how these services interact.