Uploading numerous assets in bulk consumes significant I/O resources, which may adversely impact the performance of your AEM Assets instance. In particular, if you have a slow internet connection, the time to upload drastically increases due to a spike in disk I/O. Moreover, your web browser may introduce additional restrictions to the number of POST requests AEM Assets can handle for concurrent asset uploads. As a result, the upload operation fails or terminate prematurely. In other words, AEM assets may miss some files while ingesting a bunch of files or altogether fail to ingest any file.
To overcome this situation, AEM Assets ingests one asset at a time (serial upload) during a bulk upload operation, instead of the concurrently ingesting all the assets.
Serial uploading of assets is enabled by default. To disable the feature and allow concurrent uploading, overlay the fileupload node in Crx-de and set the value of the parallelUploads property to true.