Hi there! Just passing by to add a random bit of info and to thanks @mental_offence again, seriously, thanks a lot for your dedication and help.
Yesterday to play Dragalia on BlueStacks, I had to turn on back Google Pay Services. I forgot to turn it off to play FEH today and got the awful Error 803-3001 -which also killed Dragalia, somehow-. Turned off GP services to see if if the error would go away, but nope. I used a back up I had around and somehow the error was still present both in FEH and Dragalia.
So I made a back up of the"Android" folder inside the "Engine" folder on the Bluestacks installation root and uninstalled everything Bluestacks related, cleaned up temp archives and registry with Ccleaner. Restarted the PC and installed Bluestacks again, then overwrited the new Android folder with the back up of the old installation -which is also rooted- and vualá! everything is back to normal, even Bluestacks is working faster now.
Also, doing this also works to install the game on different computers, just tried on another PC and it seems to work, even with both Bluestacks instances opened the same time, useful to share the game without the need to re-download everything again. It's seems to work like the Memu OVA, though is heavier and I don't really know what else may trigger, so have caution while doing so.
That's all, a quick fix if ever someone finds itself on my situation. Good luck!