Could be possibly because of how many relays I have on my profile? The apps cache usually gets to about 6GB each day sometimes only 3 but I have to clear cache everytime i'm done using the app for the day. Could be maybe because i'm using calyxos. Did you try it on only the android stock os I don't know if that may be the cause or not just thinking of possibilities.
Discussion
Humm... That is strange, the cache should rotate at around 2GB. This is automated by OkHttp, one of our libraries. Maybe that's the issue. The lib is thinking you have way more space to let it grow to 6GB.
Maybe only you will be able to find out & know. If it helps my user data stays at 1.01GB if that's relevant or not. I don't have many apps really on this device I got over 110GB free in storage space.
I have another question unrelated to this how do you have the url square next to your status bar?