MX Players normally works fine on most of the devices and loads up instantly so you can watch videos on it with the best experience.
Sometimes, however, while using MX Player, the initial startup takes too much time until showing the folder list. Normally, that does not happen and MX Player instantly loads up once you open the app.
This might be due to an issue with your device or storage (external SD Card) due to which this may be happening and it may be taking such a long time to load up.
Too Many Folders
One of the possible reason why this happens is that there are too many folders on your device. MX Player scans all the folders on your device to build up the video list. Therefore, if you have too many folders then it can take quite some time to scan all those folders from your device.
You can reduce the scan time by configuring the MX Player to scan only the media library folder. You can do this by going to MX Player Settings > List > Folders.
Too Many Audio Files
Your device contains too many media files (i.e audio/video files). This is a rare occurrence. You can remove some files that will reduce the launch time.
There may be SDCard or Internal Memory Error due to which the launch time will be extremely slow due to slow reading. In this case, formatting the SDCard/Internal Storage may be the best option.