Thanks for reaching out to us. I can provide some insight regarding the missing Activity section on your invoice in QuickBooks Online.
We received similar reports from other users like you, and our Product Team is aware of it and currently looking for a permanent fix.
If you want to know when you send the invoice, you can check the Audit History of the transaction. However, there is currently no workaround to see the messages posted by a client or the Viewed date and time.
In the meantime, I suggest giving our Customer Care Team a call to add your account to the list of affected users. Please have our representative link your case number to INV-27731.
An email will be sent to you with any new information to assure you're up to date with the progress of the investigation. Rest assured, I will also keep you posted here in this thread for any updates available.
Here’s how to contact phone support:
1. Sign in to your QBO account.
2. Go to Help at the top right.
3. Click Contact Us to connect with a live agent.
That should do it. Please let me know how the call goes. If you need anything else, leave a reply below. I’ll be here to help you out. Thanks for dropping by and take care!