Google Pixel user here with version 6.6.4 of Message+.

When someone sends a group text to me that wasn't created in Message+, I see "Downloading" in the senders individual thread.  If others reply, I will see "Downloading" in their individual thread.  It will usually eventually show up correctly (as a group text).  This can take minutes, or hours or days.  Sometimes killing the app and launching again can trigger the download to complete.

This is not specific to this device.  It happens to a couple of other phones I have on Verizon.   I have trued changing: "Enable Chat", "Auto-Retrieve", "Group Conversations".

How can I fix this?

Thanks.