Currently using Windows 10, 22H2, Thunderbird 115.12.2. This PC has been working fine since it was built approximately January of this year, 2024. I have not installed any new software or made any major changes for several months. I'm using Bitdefender Total Security. Recently I started noticing this issue with Thunderbird (I've been using as long as it's been out.) When composing a message, I now see on a regular basis at the lower left of the message window "Assembling message......." or "Assembling message......... Done". Thunderbird does not crash. If I continue to compose and send, the message always sends. So I'm not having the error some others have had in the past. But it does look like the message I'm typing may be having issues being put into the Drafts folder while it's being composed. That seems to be the only operation happening when the message appears. I have seen this past week the messages sending and being placed into the Sent folder but there have been at least two messages identical to the ones sent that are still in Drafts and are not deleted after being sent. So whatever is going on seems to be a bug with the saving of the draft and then cleaning out Drafts after the message is sent. Note these are text only messages and I did not change any settings in Thunderbird after updating last week. While Bitdefender updates on a regular basis and Thunderbird notifies me of updates when they are available (same with Firefox), those are the only items being updated so it seems something is going on. I am going to assume this is an issue with Thunderbird for the time being since nothing else has changed. I've gone through tips noted for those having errors sending messages when they get the Assembling message notification but I don't get any errors. Just a weirdness with the Drafts folder. In the interest of safety, I don't want to turn off AV to test anything. I've also compacted folders to no avail. Seems that notification keeps coming back. Any additional help would be appreciated.