Issue when doing data export

Tried testing the data export function and got the following issue with one of the custom profile fields on export. Running MYBB 1.8.15 and PHP 7.1.9

Fatal error: Uncaught DOMException: Invalid Character Error in D:\non_game_servers\wamp\www\devildogs\inc\plugins\amnesia\core_portability.php:300 Stack trace: #0 D:\non_game_servers\wamp\www\devildogs\inc\plugins\amnesia\core_portability.php(300): DOMDocument->createElement('Main Callsign') #1 D:\non_game_servers\wamp\www\devildogs\inc\plugins\amnesia\core_portability.php(305): amnesia\appendArrayToXmlElement(Array, Object(DOMDocument), Object(DOMElement)) #2 D:\non_game_servers\wamp\www\devildogs\inc\plugins\amnesia\core_portability.php(194): amnesia\appendArrayToXmlElement(Array, Object(DOMDocument), Object(DOMElement)) #3 D:\non_game_servers\wamp\www\devildogs\inc\plugins\amnesia\hooks_frontend.php(239): amnesia\outputUserPersonalDataXml(1, true) #4 D:\non_game_servers\wamp\www\devildogs\inc\class_plugins.php(142): amnesia\Hooks\usercp_start('') #5 D:\non_game_servers\wamp\www\devildogs\usercp.php(57): pluginSystem->run_hooks(Array) #6 {main} thrown in D:\non_game_servers\wamp\www\devildogs\inc\plugins\amnesia\core_portability.php on line 300

Not sure why it is complaining about invalid character. This is a plain text profile field.