I am trying to left-click my NPC to run a command. I am running version 1.8.7, on the Paper version 1.11.2.

I have set it to both when doing /npc cmdadd --f Both time - and in my config.yml file. Right-click works fine, however left-click does not work at all.

I know this thread is closed and very old, but I ran into the same problem. For me it was Multiverse-Core causing this issue.

To fix it, stand in the world where you want the NPC's left click command to work and type
/mvm set pvp true

If you still want PVP to be disabled in the entire world, use worldguard and type
/rg flag __global__ pvp deny

Left click then works as intended.

Is the NPC a villager? If so, what other plugins do you have?

The NPC is a default NPC with a set skin. I have a lot of plugins, however not any that I think would cause an issue. Major one is Featherboard. I will look in a few hours and list more plugins.

I suppose I might just have to disable every plugin one by one.

I'm thinking this has to be an issue with the incompatibility between this plugin and another as there is no one else having this issue. And this would be a major issue if it were lol

So I have looked at all my plugin, and they are all pretty basic, and I don't believe I have any plugins that do anything with the hand either. -with the exception of a plugin I coded for player information, however, it only checks when the command is run.

Do you have a list of possible known issues with plugins?

I honestly have no idea why it wouldn't work. The only plugin so far that has caused conflict with this is 'Bar Gamble,' and that's why I asked if you used a Villager as the NPC.