Thunderbird slow opening emails in large folders after recent BitDefender update
After a recent BitDefender update that required restarting the PC, Thunderbird has got slow opening e-mails in any large local folder, such as with a few thousand e-mails or over 1GB in size. For example, my Inbox (a basic local folder, not IMAP or synced) is 3.7GB and any unread e-mail I open shows "Loading Message..." for about 8 seconds, regardless of whether the e-mail has attachments. During this waiting time Task Manager shows Bitdefender Virus Shield using a steady 14.5% CPU. Marking e-mails as Unread/Read in large folders has the same effect. When I disable Bitdefender Shield, e-mails open instantly like before this recent BitDefender update.
I tried reinstalling BitDefender and the problem went away temporarily. About an hour later a pop-up said BitDefender needs to restart my PC to finish an update. After I rebooted, this issue returned.
I'm using the BitDefender Free Edition (Build 26.1000.32.77), Thunderbird 102.9.1 and Windows 10 Pro x64 22H2. PC is a HP Z240 with an Intel 7700K i7 CPU, 1TB Samsung 970 m.2 EVO SSD and 32GB of RAM.