Blazor WASM multiple dropdown virtualization doesn't show all items

Hi, I'm working on a multiple dropdown with Blazor WASM, I get data from backend API, but LoadData event was only triggered twice: first time when I typed in the condition (I get 8 items), and second time when I scrolled down to the bottom of the dropdown and scrolled back a little (I get 16 items), after that LoadData was not triggered at all.

As the second and third images shows, I have 29 items from API, but the virtualized dropdown only shows 16 items, wondering does Radzen Blazor Server and Blazor WASM have different virtualization way?

There's another issue, when I selected any item, and LodaData is triggered, there'll be error: Unhandled exception rendering component: Collection was modified; enumeration operation may not execute.
System.InvalidOperationException: Collection was modified; enumeration operation may not execute., not sure why does it happen, would you give me a hint?

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