The reason I no longer parallel charge is I have had several batteries over the years where a single balance tap wire has come adrift within the battery (so not obvious) or there's a balance connector issue. When series charging that is seen immediately as a cell mismatch however, as Vince has said during parallel charging this could be masked due to the cell averaging. I do now strain relief the balance tap wires and have not had a failure since. Also I monitor the individual cell IR's every time I charge, again with parallel charging you can't get this, just an average IR of all cells in parallel.
Steve