UK Clock Change Issue

Hi, Here in the UK we’ve just put our clocks back one hour for the winter. What we have since noticed are strange entries into SQL from Transaction Groups. The groups are basically storing an incrementing value and determining the difference between now’s value and the previous one a minute ago (SQL TOP 1 query).

Looking back the data only starting going wrong from the clock change time.
A reboot of the server has cured it but I’m looking for an explanation if possible.