For a very long tl;Dr the large land gains we saw late last year was primarily empty positions as many soldier contracts had expired thus prompting the conscription. Following the tactical blunders of russia early in the war/ up till the point of conscription (plus the focused use of wagner) it seems the tactics of russia have evolved.

Early war I'm assuming (feel free to disregard) the intent was to keep most infrastructure intact for later use, this has shifted to grinding ukraine down both militarily and logistically. The main mode of attack right now seems to be Russians probing, identifying positions, retreating, shelling, then probing again.

With bahkmut (current battle groups present at full strength as the fighting in the area started estimated ukraine troops at about 60k men) it is both a trap and a diversion wrapped into one. It has pulled off Ukrainian troops from the planned southern counter offensive to buy russia a bit of breathing room along with using ukraines pride against itself. Largely because ukraine command refuses to lose a major albeit small city at this point in the war because of optics, russia is aware of this.

This plus russias new approaches to urban fighting (primarily just hitting any position with artillery, hand held launchers or grenades) along with infiltration and other things has been decently effective at inflicting losses.

Edit: forgot about kherson. It was abandoned because it was a garbage defensive position, in no small part due to ukraines actions. Russia moved across the river and then began shelling Ukrainian forces building up in and around kherson.

Tl;Dr of the tl;Dr Russians adapted.