1. Switch Keyboard Layouts
After trying many things the most untechical solution, just switching keyboard layouts to another language and back (DE->EN->DE for me) has surprisingly worked.
2. Try to disable scroll lock manually
Via the accessibility feature
Try to enable the keyboard screen-overlay in the accessebility settings, on some versions there might be a scroll lock key, sometimes there are just the letters.
On xfce Desktops
sudo -H gedit /etc/default/keyboard
remove: grp_led:scroll
from XKBOPTIONS="grp:alt_shift_toggle,grp_led:scroll"
On gnome desktops
remove: 'grp_led:scroll'
from
dconf read /org/gnome/desktop/input-sources/xkb-options
by executing
dconf write /org/gnome/desktop/input-sources/xkb-options "['grp:alt_shift_toggle', 'numpad:microsoft']"