I need to query items in a given folder and all of its children in a document library with as few APIs as possible.
The ideal solution seemed to be getItems with Scope='RecursiveAll' and a FolderServerRelativePath. However the API below returns an SPQueryThrottledException for a specific document library on Sharepoint Online, and I can't figure out the reason.
POST <web-url>/_api/Web/Lists(<list-id>)/getItems?$select=*,FileRef
POST BODY:
{
    "query": {
        "odata.type": "SP.CamlQuery",
        "ViewXml": "<View Scope='RecursiveAll'><RowLimit>1</RowLimit></View>",
        "DatesInUtc": true,
        "FolderServerRelativePath": {
            "DecodedUrl": "<subfolder's-server-relative-path>"
        }
    }
}
Some observations:
- The subfolder has 4 files and no folders in it.
 - Getting items under any folder in the document library fails with the same error
 - The document library has around 6.5k items (folders+files) in it
 Scope='Recursive'also fails, but'Default'and'FilesOnly'work fine- The same query worked for another document library with 100k files
 
What's the problem with the query? How can I fix it? If it's impossible to fix, are there any other APIs that can recursively query items in a folder?