Have you IPL’ed since you shifted over to summer time? Maybe there’s a job still running which has winter time as an attribute?
My first question would be “How did you implement the summer time QTIME shift?”.
IFS times are internally stored as a UTC value and being off by an hour suggests that the internal UTC based clock is also off by an hour. This could be caused by someone using CHGSYSVAL QTIME to alter QTIME by an hour in order to reflect daylight saving time, or someone using the time adjustment capability of the system to adjust local time by an hour. The correct way to implement summer time is to have the correct time zone (correct in terms of DST rules and UTC offset) specified in the system value QTIMZON — in which case summer time start and end is automatic.
I seem to recall that IFS does, for historical reasons, maintain time related information in a cache which may not be immediately updated. But the update would be within an hour (worst case) of the summer time transition.