Thanks for reporting the bug, but we won't be able to fix it.
The bug isn't in just URP. It's a hard limitation of D3D11, which supports max 16 active samplers. Active here means used in one shader. There's nothing we can do about it directly.Also it's not about "light cookies" it's just the last feature included pushing the total above the limit. Only way to fix it is to reduce the number of samplers somehow—maybe by using less keywords that use texture samplers, or maybe by switching to an API that doesn't have the limit.