I have a list with ~6200 items. I can query these items without any performance issues, but if I try to update them or create new items, it's going very slow.
When I try to update them via
ClientContext.ExecuteQuery(), I'll get a timeout error.
If I update them through PowerShell, the execution of
$item.Update() takes forever. Same behavior, when I click "Save" in the New Item- or Edit-form, but after a few minutes, the items get updated/created in the background.
The list has a total of 28 columns and no lookup columns (except the default Created By/Modified By columns).
I have other lists with even more items (up to 20000), but fewer columns, which are working fine.
ULS log contains no errors, when I try to save an item.
The lists inherits it's permissions from the parent site collection.
The List View threshold is set to 25000.
I've also tried to save the list as template and created a copy of the list, but it led to the same behavior.