It seems to be happening between fields not just line breaks
Here is my site:
ArcGIS Web Application
What my popup is configured to show.
{MAPNUMBER} {TAXLOT}
{FEEOWNER}
{ADDRESS1}
{CITY}, {STATE} {ZIPCODE}
Result (not a real result but what is happening)
{MAPNUMBER}Â {TAXLOT}
{FEEOWNER}
{ADDRESS1}
{CITY}, {STATE} {ZIPCODE}