Hello, I had this same problem. I set some debugging and found that my multi site install is failing after the images are uploaded in this function where it tries to unset the directory cache. From another forum I found that I dont even have WP set to use transients. I’m using WP 5.8.3 and PHP 7.4.3 with mysql 8
// while ( DIRECTORY_SEPARATOR !== $path && '.' !== $path && '..' !== $path ) {
// $path = dirname( $path );
// unset( $directory_cache[ $path ] );
// }
comment out lines 8178 to 8181 in functions.php then it will work.
I am not quite sure if this fix will cause any other issues? I am hoping you guys could help with that part?