@ ActiveX
What operating system have you got ?
If Windows 10, the Flash Player update (ActiveX version) is handled by the Windows Update, that could possibly be the issue.
That said, checking my Avast Software Updater, it also showed Flash Player ActiveX version (Windows Update), it also showed Thunderbird needed an update.
I had only intended to update Thunderbird and clicked the Update tab for that, but it also Updated the ActiveX Flash player and now the software updater reports it as being up to date.
That said 2: I'm not running the 17.7.2314 version of avast free.