Changes to the theme don't apply

[Bernardo Oliveira]

When I try to apply a theme it just doesn't apply and resets to the default. (GIF -> https://prntscr.com/rh3foy )
When I run plank from the terminal I get this error:

[WARN 10:35:27.626794] [Preferences:192] '/usr/share/plank/themes/Default/dock.theme' is read-only!

I don't know what could be causing this issue. If you need more information I can provide you with

OTHER INFORMATION:

-> output from running plank -d : https://pastebin.com/1FAgayeb
-> plank version: 0.11.4
-> linux distro used: Xubuntu 18.04
-> window manager xfwm4
-> X version: 1.20.5
-> desktop Environment: Xfce
-> video card: 01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] RV710/M92 [Mobility Radeon HD 4530/4570/545v]
 Subsystem: Toshiba America Info Systems RV710/M92 [Mobility Radeon HD 4530/4570/545v]
 Kernel driver in use: radeon
 Kernel modules: radeon
-> installation method: sudo apt install plank