problem

When using the page-down or page-up button, there are always a few segments missing (meaning the grid skips them on scrolling).

Reason

The handling of page up/down in the grid is done by the onKeyPageDown and onKeyPageUp methods in the class Ext.grid.NavigationModel.

In both methods getRowsVisible is called to calculate how many rows should be scrolled.

I traced the output a little bit, the calculated values are sometimes not really useful. Also there is a comment:
"This assumes that  all rows are of the same height" which is false in our case!

So my assumption to the reason is, that the getRowsVisible function is just calculating wrong row count, using somehow a average or fuzzy value for the row height.

solution

Rebuild this function, based on the real count of shown rows instead of the "fuzzy" value.

Updating ExtJS is currently also no solution, since in 6.2 the affected functions are still the same.