Transaction Group "Timer" shifting?

Don’t really know what is going on but on occasions, I have seen on a trend graph a blank spot of maybe an hour. If I go back and look at the database I can see where the data trigger(1 Hour Timer) shifted.

Example: today I started and a new table with data being recorded every hour starting at 7:20 and for the next 11 hour it was right on but then it missed the 18:20 trigger but restarted at 19:00 and continued from there on the hour.

the transaction group says “warned”.

Can anybody shed some light on this matter for me?

Sorry this is version 7.9.10