I just confirmed on one of my 2013 environments that the incremental/full scheduled crawls keep getting delayed inexplicably since I canceled one of them earlier this week that had run for too long. The last completed crawl was several days ago and since then it has said crawls were planned for the same night, but those crawls never kick off and the next day it says the crawls are scheduled for that night instead. This has happened three times in a row with no crawls being executed at all. Has anyone seen this behavior before?
Edit: Examining the ULS logs shows a rapid string of SQL connection errors. Checking the SQL server itself revealed no errors on that side, so I just rebooted the SP server and everything magically went away. But now... the Timer Service is eating up 75% of the CPU power. I guess that's a separate question.