End users are unable to write comments on RITMs for Requests created for someone else
This behavior is seen because of a table level write ACL on the 'sc_req_item' table. This ACL has a condition which checks if the Request.Requested for field has the same user as the user accessing the RITM. If the end user created the Request on behalf of someone else, this condition will fail and the user does not get write access so they are unable to write to the comments field.
To resolve this issue, i.e. to allow end users to be able to comments on RITMs created for Requests they created on behalf of someone else, a new write ACL can be created on the 'sc_req_item' table and instead of checking for the 'Request.Requested for field', the ACL can check for the 'Opened by' field to match the user accessing the record.
Please note: Removing the condition in the existing ACL would make the RITMs open to write access to all end users as this ACL has no role restrictions.