If a repair doesn't work:
Try running a clean install - use the installers I linked.
1.Download your version of avast and the avastclear tool - save them to the desktop:
Avast Free AntivirusAvast Pro AntivirusAvast Internet SecurityAvast PremierDownload
Avast Clear Tool2. Uninstall Avast from Control Panel (if possible) and reboot.
3. Uninstall in safe mode using Avastclear. [Running Avastclear is normal mode will give a prompt to go into Safe Mode] - If you are unable to run Avastclear in safe mode, run it in normal mode
4. Install the version you downloaded.
5. Reboot.
Paid: If you have a paid license, insert the license key/activation code after the reboot at stage 5.
If that doesn't fix it, it's most likely a bug introduced in v18.7 which I will get reported after I get your reply.