Your upload setup doesn't happen to include a hidden field that is telling Lawson to ignore warnings, does it? Unless you are using a version of the add-ins different than ours, it makes exactly one attempt to upload the record.
That's the equivalent of hitting whichever button on that form counts as 'submitting' the data. If the data itself would cause Lawson to return a warning or an error, then that gets pushed to the results field and the add-in moves on.
The exception to this are the forms which have hidden keys in them, which often are used by Lawson to track whether or not it should show you the error/warning or if it's already done so and can assume that you are clicking 'submit' twice to force the update.
Unfortunately, PR35.2 is locked down on our system to the Payroll team, so I can't see what fields are on it. But I suspect it's one of those forms and the probelm is that your upload is currently set to tell Lawson that it shouldn't be telling you about those errors via a hidden key.