Not sure if this is a known issue or just on my end, figured I'd post my findings for posterity.
When my loot filter is too long, entries after a certain length down the list get cut off. For example, with the Elementling filter pinned on the Discord, I can't scroll any lower than "Hide: Tier 2". If I delete a few entries, I can get a little further down, maybe one more entry. If I scroll all the way down, export to clipboard, open the filter in notepad++, copy and paste most of the items in twice (so the filter gets significantly longer), import from clipboard, and switch back to the Elementling filter, I can scroll up to see the last dozen items, and once I've done so I can't scroll back down.
It may be a coincidence, but the issue occurs around 3000 lines of code/text in notepad++. To my knowledge I don't use D2GL. This occurs whether rendering with DirectX or Glide+Glide3x.dll.