Not able to Update/add new roles OR assign

In GUI: Recently we have faced couple of times to edit/add new role and/or assign the users to a Role-Name.

• But able to add new users and assign role thru (Python API).
  After able to delete one/two role name(s) then able to add new users.

Are there are any limitation for number of role and/or number of users to add into configuration. And/OR - are there any possibilities to increase this limitation(s).

Looks like Jenkins just save each every login attempt (under '.jenkins/users' folder), can I delete the junk ones.!? May be these junk ones are adding to the max-limitation(s)... Example -
[$]# grep 'you' you_3382053529920276951/config.xml
<id>you</id>
<fullName>you</fullName>
<emailAddress>you@example.com</emailAddress>