I have a Cisco 435 that nearly always has a delay when changing channels, searching for a signal for a second or two in between. I tried rebooting and "Fix Fios TV Issues".
This started a few weeks ago.
DO you have more than 1 box?
If so, does it happen on all or just the one?
If it is only one of several, then try swapping them around to see if problem follows box or connection.
If it is all, then start at ONT.
Make sure all coax connections are tight.