I have dealt with a similar issue before. Maybe this helps you with your problem.
I had to increase the range of all conditional formats on a sheet.
I had to increase the range of all conditional formats on a sheet.
IXLConditionalFormats condFormats = worksheet.ConditionalFormats;
foreach (var format in condFormats)
{
format.Range = worksheet.Range(format.Range.RangeAddress.FirstAddress, newCell.Address);
worksheet.ConditionalFormats.Add(format);
}