Fix the NaN issue and revert the reversion

config/sections/files.php

@@ -194,14 +194,14 @@
 				'multiple'   => $multiple,
 				'max'        => $max,
 				'api'        => $this->parent->apiUrl(true) . '/files',
-				'attributes' => array_filter([
+				'attributes' => [
 					// TODO: an edge issue that needs to be solved:
 					//		 if multiple users load the same section
 					//       at the same time and upload a file,
 					//       uploaded files have the same sort number
 					'sort'     => $this->sortable === true ? $this->total + 1 : null,
 					'template' => $template
-				])
+				]
 			];
 		}
 	],

panel/src/panel/upload.js

@@ -289,8 +289,10 @@ export default (panel) => {
 				// add file to upload queue
 				files.push(async () => await this.upload(file));
 
+				const sort = this.attributes?.sort;
+
 				// if there is sort data, increment in the loop for next file
-				if (this.attributes?.sort !== undefined) {
+				if (sort !== undefined && sort !== null) {
 					this.attributes.sort++;
 				}
 			}