So when an AFV gets smacked by a Stugna/Javelin etc, the entire squad is killed?
The reason the Russians are getting sandbagged is because they aren't doing combined arms; In some areas they have tanks, and infantry, but no artillery coordination. Arty is the best counter to ATGM teams, but you have to have the barrels, the field observers to aim it, all in coordination with the tanks and infantry (so you don't smack them). In other areas they have tons of infantry and artillery, but no tanks so they can't really advance.
Russia's BTG design isn't really around tanks, but instead AFVs. They use tanks as fire support for infantry, but the average battalion only started the war with around 10 tanks (vs 40 IFV). Of course some units were understrength, (and now much worse).
This makes the BTG very brittle when opposing forces have matching tanks and good ATGMs. Combine this with poorly trained infantry, and all those IFVs are just wasted.