[Baertram]

There isa server-wide max keybind number ~200!
Try to disable all other addons, then only enable the one here and set the keybind. Most of the time too many addons adding keybinds will make the keybinds save "visually" for the session, but after a relaodui/logout the server didn't save them, due to this hidden max keybinds boundary.
So disabling addons and trying to check if the keybind works with ONLY this addon in question will show you if it's the server, or the addon causing the problem

If it's the server: You need to set the keybinds then with only a few addons enabled and after setting it reenable the addons you want to use.
Does not work at all times. Sometimes you even need to enable addons in packages and disable the set keybinds so the slots are free again and can be used for other addons.
You can use an addon manager/profile manager like "Addon Selector" to help you here.
You are able to enable/disable many addons by clicking one line and then SHIFT+left click another line below e.g. to "block mark" and enable/disable them.