We want to use the header summary where we show years with months and a summary of a year. but it seems that in combination with the setTimeSpan it draws a lot of lines and not showing the summary propery as a year but as days.
it can be reproduced in the online example at:
https://bryntum.com/products/scheduler/examples/header-summary/
by changing the header units in the examle to year, month and year and adding the following line:
scheduler.setTimeSpan(new Date(new Date().getFullYear() - 20, 0, 1), new Date(new Date().getFullYear() + 50, 0, 1))