Struggle showing monthly open

Hello guys,

I made this little script to plot the monthly open on my chart :

study(title=Monthly Open, shorttitle=Monthly level, overlay=true)
smh = input(true, title=Show Monthly Open?)
mtdo = security(syminfo.tickerid, 'M',open)
plot(smh and mtdo ? mtdo : na, title=Monthly Open, style=plot.style_circles, linewidth=4, color=color.silver)

it doesn't work well as there is a day gap between the monthly open and the plot. Does anyone know why ?

Thank you !

Do this

s2=security(syminfo.tickerid, "M", open, barmerge.gaps_on, barmerge.lookahead_off)
plot(s2)