These are not 1980's Iran-Iraq style human waves. It's a couple of squads advancing. Twenty men or so. Media love the term though.
It is a “shock troop” tactic, where the small groups are conducting reconnaissance in force from behind the artillery barrage, then return at night to finish off the defenders.
Has been this way since WWII hence the stories of “Russian hordes” by old and new Nazis.
Wagners use groups of 8 expendables to probe several points simultaneously - when a surviving group or individual finds a weak point, the contract Wagners are sent in.
That way they save their best fighters, but loose a lot of expendables (convicts). Badly wounded are left to die.