I can't shutdown of the tails OS

Environment:

tails 2.2.1
dell inspiron 15 3000 series
legacy mode(boot)
this os is installed from ubuntu
there is persistent volume

After shutdown, a lot of string was streamed until forced end.

For example:

   ［ 0.000123］   ［］ ? *****
        .
        .
        .
   ［ 0.504123］   ［］ ? *****
        .
        .
        .
   ［ 2065.058658］［］ ? *****

(* is unknown. very fast.)

What should I do?