It's probably working just fine. The part that looks wrong is inside Plot
where possibly low precision is being used. Instead try this.
(1) Do not set $MinPrecision
or $MaxPrecision
.
(2)
ListPlot[Table[Im[fdis[[Lambda]0t, nR, d1t, d2t, d3t]], {nR, N[19/10, 100],
1999/1000, 1/1000}]]!
Alternatively:
Plot[Im[fdis[\[Lambda]0t, nR, d1t, d2t, d3t]], {nR, N[19/10, 100],
1999/1000}, WorkingPrecision -> 70]
These look smooth to me.