Hey!
What software are you running?
I found the following bug:
https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvr97004
Symptom:
Unable to configure VTY lines higher than 5 on an ASR920 running 16.9.4
Workaround:
This behavior is not seen on 16.6.3, 16.9.3, or 16.11.1a
If you are not running IOS-XE 16.9.4 - can you please post what exactly you are configuring?
Best regards
Julian
P.S. please reate helpful posts or mark solution if applicable