Hogging space on Android phone

Hi. The other day, after about 2-3 months after I installed Discord on my phone, I received a notification about low storage space on my old tired phone, like I do from time to time.

I, however, noticed that the Discord app was storing stuff on the internal memory, and there was the option to move it to the SD-card, so I did that.

To my surprise, it was storing a whopping 1,5 GB of stuff. I don't know if this is some form of cache-function, as I've only received memes along with the rest of the users on the servers I'm in, but I can't recall receiving any files personally, nor have I sent any, as I'm using the PC-app for any such stuff. Perhaps it uses the phone app to copy over that data. Although I can't remember sending either much data, nor big files that could amount to that space.

The issue here, however is that any and all such data should be saved to the SD card IMO.
I'm aware of the limitations for notifications vs. storage-deal. Meaning that in order to run certain functions, which I can't quite recall at  the moment.

I think it must be possible to write some code that can move any such data to another location or some other way to at least flush the stored items.

I just tried the flush-function in the settings for the app, which requires me to recreate the login-credentials. Not a big deal, but I don't want to keep doing this each time.

I hope that this wasn't moved because of where it was stored, and couldn't be moved to the SD card (Android 6 btw) due to some limitations perhaps?

My phone gets really slow when the internal storage gets maxed out, and it fails to retrieve emails and SMS.

It's due for an upgrade for sure, but non the less, this issue I feel should be addressed.

Thank you.