Comments can be viewed by anybody who had permission to view the contract when the comments (or replies to comments) were created.
Members of your organization can see all Comments for the contracts they have permission to view. Suppliers can only see comments & replies to comments that were added to contracts after the Supplier was invited to the contract.
Here is how to check if a supplier can see a comment:
- Open the comment to see the date/time stamp for when the comment was added
- Open the Contract History > Full History to check the date/time for when the Supplier (external user) was invited to the contract
- If the comment was added after the user was invited, then they cannot see it.