My interpretation of this is that your scheduled searches are being hung for some reason. I would typically assume this means the necessary resources are being consumed by other searches, but you only have one lagged search, which is interesting. Additionally, it is "non high priority", so hopefully that means this isn't an enormous issue.
EIther way, you should be able to investigate this (assuming you're a Splunk admin on your instance) by going into Settings -> Monitoring Console -> Search -> Scheduler Activity: Instance, and inputing the timeframe when this occurred. Hopefully the information under "historical charts" can point you in the direction of what caused this to occur (perhaps the machine blipped, etc), or at least narrow down the timeframe/options so you can continue debugging.
