Toggling to Local time does more than rotate the hour-of-day charts. Each data point is re-binned into the wall-clock hour it actually occurred at, which means samples cross Daylight Saving Time boundaries differently depending on when they were recorded.
For example, a sample at 11:00 UTC in August (EDT, UTC−4) lands in local hour 7, while the same 11:00 UTC in December (EST, UTC−5) lands in local hour 6. So the UTC and Local hourly charts are not simple rotations of each other. The sample mix inside each bin changes. This is the intended behavior: it answers the question "what does my activity look like at 7 AM my time," consistently across DST transitions.