I'm not sure how the avast webrep works across different firefox profiles, but the additional protection, browser protection, Firefox, would I guess apply to all profiles as it is still firefox.
I don't know in the profiles that aren't working, if you open the add-ons and see what version of the webrep add-on is reported as installed. Possibly those not working are reporting 7.0.1473 version of webrep. If so uninstalling webrep in those profiles and also in avast additional protection, browser protection, Firefox, so it is removed. I would restart firefox and reboot, then install the webrep again in additional protection, browser protection, Firefox.