Timeline preview render issue

Hi,
if I had put a transition or any other effect on my current timeline resolve started automaticly a render process for that particular area of my timeline.
But now it doesn't. Maybe I switched it of by mistake. However it doesn't work anymore and I have no idea how I can fix that.
Are there anyone who can help?
Thanks
inetd1910
if I had put a transition or any other effect on my current timeline resolve started automaticly a render process for that particular area of my timeline.
But now it doesn't. Maybe I switched it of by mistake. However it doesn't work anymore and I have no idea how I can fix that.
Are there anyone who can help?
Thanks
inetd1910