Would help, next time, if you were to give some examples of file sizes - a video file and especially a .mbz backup file.
Possible that some PHP settings need to be increased.
Go to Moodle admin -> server -> php info -> Section labeled 'Core'
Look for variables and their current setting for
post_max_size, upload_max_filesize, max_input_time.
post_max_size, upload_max_filesize higher than the largest file you are attempting to upload.
max_input_time is probably 30 seconds ... increase to 60.
When changing settings for PHP, web service must be restarted.
Also check the settings in courses for upload size limits.
Restoring backups might require a tweak upwards in php for max_input_vars also.