Jira only displays the first two transitions as buttons. You can change this setting by editing the ops.bar.group.size.opsbar-transitions property in the jira-config.properties file located in your JIRA_HOME directory.
All you have to do is edit the file, set the property to the desired number of transition buttons to display as shown (we are setting the number of transition buttons to 3), and restart Jira:
ops.bar.group.size.opsbar-transitions=3
If you do not see the jira-config.properties file, you can simply create a new file with the same name and add your properties there.
See the following screenshot:
Jira now shows three transition buttons instead of two.