When using NEI, trying to type into the Allowed Players GUI, NEI overrides the keypress and opens NEI specific GUI's. When using this mod with NEI, use 'ctrl + o' to disable JEI/NEI and allow yourself to enter the name correctly. This is a problem with NEI not Dimensional Pockets II. Once the issue is sorted within NEI I will close this Issue. NEI hasn't had an update since august 2019 so I am unsure as to when this will be fixed.

So I have received a response from NEI developers, 1.12.2 is not being supported any longer. This issue will likely not exist when the I update DP II to 1.14.4

FIX: Holding 'ALT' while pressing the desired key will stop NEI from overriding the keypress.