I have a grid that binds data with the async pipe, and it subscribes to the dataPreLoad pipe for scrolling and adding new records into the grid. For example, a grid source has 300 records, loads 25 initially and every time I scroll to the last chunk, it'll load 25 more and the scroll bar will resize accordingly. If scrolling happens too fast and exactly at wrong times, some sort of race condition occurs where the scroll bar will disappear. This is hard to reproduce, happens maybe 1 of 5 times and have to be scrolling very fast.

What I traced it to is the individualSizeCache property of verticalScrollContainer gets undefined values in it, which happens in handleCacheChanges() when it tries to update with item.previousIndex, but previousIndex actually gets higher then the length of individualSizeCache, so you get undefined. Seems like perhaps initSizesCache does not run before handleCacheChanges to push the newly scrolled into items? If it is a race condition and incredibly sporadic, I could see this being the case.

Would it make sense to set the default size (in the else condition) if this happens, or is there something I can do in the implementation to prevent this? I included a screencap with the items in the watchlist that show how this would occur.