That would happen if Excel was opening the files as text rather than recognising them as CSV files.
What is your regional list separator? Is it different from the separator in the CSV file?
The code worked perfectly for me (with comma in both cases).
Replace
Set WB = Workbooks.Open(stPath & stFile, ReadOnly:=True)
with
Workbooks.OpenText stPath & stFile, dataType:=xlDelimited, comma:=True
Set WB = ActiveWorkbook