External Content Protection not working always

Example: Demo site (demo.sgalinski.de) / demo page

All YouTube videos are rendered, because the MutationObserver is not working here. Seems like it must also check childs. Even by doing this, I couldn't get it working. See some test code. This is extremely slow. You can see it also here: https://www.benediktbeuern.de/wandertouren

		// Create an observer instance linked to the callback function
		iFrameObserver = new MutationObserver(function(mutationsList, observer) {
			// Use traditional 'for loops' for IE 11
			for (var index in mutationsList) {
				var mutation = mutationsList[index];
				if (mutation.type !== 'childList' || mutation.addedNodes.length <= 0) {
					continue;
				}

				for (var addedNodeIndex in mutation.addedNodes) {
					var addedNode = mutation.addedNodes[addedNodeIndex];
					if (addedNode.children.length > 0) {
						for (var childIndex in addedNode.children) {
							var childNode = addedNode.children[childIndex];
							if (childNode.children.length > 0) {
								for (var childIndex2 in childNode.children) {
									var childNode2 = childNode.children[childIndex2];
									if (childNode2.children.length > 0) {
										for (var childIndex3 in childNode2.children) {
											var childNode3 = childNode2.children[childIndex3];
											if (childNode3.children.length > 0) {
												for (var childIndex4 in childNode3.children) {
													var childNode4 = childNode3.children[childIndex4];
													if (childNode4.tagName === 'IFRAME') {
														replaceIFrameWithConsent(childNode4);
													}
												}
											} else if (childNode3.tagName === 'IFRAME') {
												replaceIFrameWithConsent(childNode3);
											}
										}
									} else if (childNode2.tagName === 'IFRAME') {
										replaceIFrameWithConsent(childNode2);
									}
								}
							} else if (childNode.tagName === 'IFRAME') {
								replaceIFrameWithConsent(childNode);
							}
						}
					} else if (addedNode.tagName === 'IFRAME') {
						replaceIFrameWithConsent(addedNode);
					}
				}
			}
		});

		// Start observing the target node for configured mutations
		iFrameObserver.observe(document, {subtree: true, childList: true});
	}