Thumbnails not getting deleted

[hitesh83]

Issue - Thumbnails are not getting deleted after deleting file from Server UI

Setup - Open Source installed on Linux system

Tested OS - Ubuntu Server 16.04.7 LTS , Ubuntu server 20.04 LTS, Alpine Linux 3.12

Error on terminal -

0|server | 9 Oct 14:37:29 - unable to find/delete thumbnail: Error: ENOENT: no such file or directory, unlink '/home/User_Name/media/_thumbnails/3d_wall.mp4'

Steps to reproduce
1- in browser open Server UI and upload a file e.g. "3d_wall.mp4"
2- ssh to server
3- "cd ../media/_thumbnails" folder.
4- do "ls" on terminal (../media/_thumbnails)
5- you can see random number added to thumbnails
e.g. for file "3d_wall.mp4", you can see "239_3d_wall.mp4.png"
6- go to server UI and delete same file "3d_wall.mp4" from server
7- File will get deleted and no longer seen on server UI
8- same file also get deleted from media folder of server (confirm by doing "ls" in ../media folder)
9- but in "_thumbnails" folder, file name "239_3d_wall.mp4.png" still exists as it is.
10- while delete thumbnails, server outputs above error log.