Ok thanks for explaining it .
I was able to see the subscribe button in forums here please check :
http://prntscr.com/cf4mc7
Can you please tell which one you are using?
Forums or unit comments .
Unit comments touch points for the instructor is not working properly .
this is a known
issue .
But it is working fine for me for the students .
TO check this can you please share your admin credentials and site url
in a private reply to check this at your end .