From memory i think online armor leaves a few drivers installed, if you look in device manager and click view then show hidden devices im fairly sure there were two OA drivers there.
There is also some leftovers of OA here but you will have to take ownership of the files to delet them C:\Windows\System32\DriverStore\FileRepository, you can run a search via the run bar for Online Armor and Emsisoft.
As was mentioned OA needs to be deleted in safe mode followed by two reboots to delet leftovers then run a seach for the items i mentioned and then follow ady4um’s instructions to repair avast, if the avast repair is not successful then try a clean install of avast.