Hello,
I have been trying to add Timezone support following your example https://bryntum.com/products/schedulerpro/examples/timezone/. If you add in recurring TimeRanges the scheduler freezes when recalculating the time zone and will stack a time range on top of another time range when it finally unfreezes. You sometimes have to switch between multiple time zones to get the freezing and stacking issues to appear. I tried both 5.6.6 and 5.6.7 and was able to reproduce the issue in both versions.
I am also having an issue with events growing longer when switching between time zones. I was not able to reproduce that issue in the attached test case but did notice there was an open ticket for the issue already.