On Groups panel (GROUPS Sysview command), for group TYPE EMAIL, the member field is truncated to 23 characters.
Release : 16.0
Component : SYSVIEW
The max length for this field is 64 characters, but the default length is 23 characters.
Since this field is a variable length field, it is possible to increase the size of the Members field, as it is shown on the GROUPS display, by going to the Variable Length Fields panel (VLFIELD command) and changing the Len column for GRPMembers from 0 to what ever you want, as long as it is 64 or less.