To my understanding, you are importing a CSV into a mendix persistent entity with a template matching to the entity's attribute types (integer/decimal, string, etc)
But for the integer (or decimal field) thousands grouping commas are breaking it.
My suggestions, (if possible) remove thousands grouping in the excel while exporting the CSV. If that is not an option, or you have existing files to process; I would recommend to create a non persistent helper entity which has similar attributes but all of them are as string. Then modify your existing excel import templates & microflows to use this new helper entity. This way, mendix will import our CSV without parsing / processing and create non-persistent entities.
Afterwards, you can loop over the non persistent entity list and parse numbers & strings with your own microflow.
for the thousands grouping number for example;
1) remove comma from the value string
Create String variable ($CommaStrippedValue)
$CommaStrippedValue = replaceAll($NonPersistentHelper/Value, ',', '')
2) parse it into Integer or Decimal (which ever you have in your original entity)
Create Object -> $NewPersistentEntity
Attribute Value = parseInteger( $CommaStrippedValue)