[Baertram]

Download and enable LibMapPing and try this in the chat if the blue player map pings are shown again (or maybe even before to never see them again):

/script LibMapPing:SuppressPing(MAP_PIN_TYPE_PING)

If you want to see them again use:

/script LibMapPing:UnsuppressPing(MAP_PIN_TYPE_PING)

You could try to add this to the small addon with the /slash command I had created for you.
Just define something like this:

local function togglePlayerMapPings(onOrOff)
 if not LibMapPing then return end
 if onOrOff then
   LibMapPing:SuppressPing(MAP_PIN_TYPE_PING)
 else
   LibMapPing:UnsuppressPing(MAP_PIN_TYPE_PING)
 end
end

Then add something to the slash commands like a new line with your own / command you'd like to use for on and one for off.
Maybe /pmpon and /pmpoff
And for /pmpon use the function togglePlayerMapPings(true) and for the other one togglePlayerMapPings(false)