ADB unauthorized, unable to get "Allow USB Debugging" popup

After flashing a new stock rom and fixing my soft brick I can't get ADB to work anymore. It lists my device correctly but it tells me it's unauthorized. The problem is that I'm just not getting a pop up "Allow USB debugging" to allow access on my phone.

Well.... this is a pretty common problem you might say and there are literally hunderds of threads covering this already and I've read probably all of them and nothing seems to work.

To list a few things which are definitly checked;
- Developer mode is enabled
- USB debugging is enabled
- Revoke USB debugging authorization checked, (the option isn't there because I haven't had a pop up).
- Deleted adbkey in the .android folder
- Tried both MTP and PTP (PTP was the one that used to work)
- Switched USB cables and USB ports
- Tried different USB drivers
- Used different versions of ADB, (1.0.36 used to work fine).

Stuff about my phone;
- LG G4 h815 rooted
- TWRP as recovery
- SuperSU
- xposed installed

I'm really running out of things to try and I've probably forgot to list a few things. Is there something I can do manually? Like copying the adbkey to my phone and place it in some directory?

Does anyone have a clue on how to fix this?