Hi Ihab,
Those "restart aquisition" are generated by the
ofdm_sym_acquisition block when it does not find a peak on
the correlation function he uses to detect the beginning
of the OFDM symbol. You should verify there is indeed a
DVB signal precisely at 570 MHz. To do this you may use
our "Sym Align OFDM" block (not a very nice name)
available with gr-isdbt (
https://github.com/git-artes/gr-isdbt)
and check that you see a "triangle" (please refer to the
readme, the examples, and even the issues on our git). The
symbol alignment is totally equivalent between DVB-T and
ISDB-T.
Moreover, I see several "O"s, meaning that somewhere samples
are being dropped. That does not help either. If you do not
have a very fast machine, you may use at the beginning of
the flowgraph a "Stream to Vector" followed by a "Vector to
Stream" with a very big "Num Items" (some millions).