Why does my downloaded video overwrite other videos?

[AC Question]

Hello,

I'm using a One Plus 3T. This problem just appeared out of nowhere a few weeks ago.

I have a bunch of videos saved on my Dropbox. I then download the videos on my phone. I go to the Apps > File Manager > Downloads to open and watch it.

But whenever I download a new video onto my phone this video overwrites all the other videos that are on my phone already.

Let's say I have saved on my phone:
video1
video2
video3

But whenever I download a new video (video4), suddenly all the other videos would become video4.

So I would basically have
video4
video4
video4
video4

(Of course the naming stays the same old only the content changes)

How do I fix this issue?