I am also facing similar issue:

mask_t = dataTable["Col1"] == "T"
mask_noTime = dataTable["Time"].isna()
diaTable = dataTable[mask_t & mask_noTime ]
diaTable["Secondary"] = diaTable["Secondary"].fillna("")
diaTable["Primary"] = diaTable["Primary"].fillna("")
diaTable["Direction"].fillna("", inplace=True)
uniqueFigures = diaTable["PlotId"].unique()

for uniqueId in uniqueFigures:
  # do some processing with the unique ID.
  pass

It runs normally without debugging but only facing this issue when trying to debug.