The usual reason for this, especially after a retune, is that you are now tuned to more than one transmitter and the Humax is watching the wrong transmitter for the start signal.
For how to tune to 1 transmitter you will need to do a manual retinue that is aimed at just 1 transmitter. To manually retune see Martin’s tuning instructions for the HDR-FOX T2, the 2000T manual tuning method is identical: https://myhumax.org/forum/topic/transmitters#post-2336
If you think you gave already done that then have a look at the signal detection menu as that will confirm which frequencies you really are tuned to.