[Paulus_PAK]

Referring to the incident at Zyelenpilye, apparently ukrainian units cought there were battalion sized battlegroup from 79th Airborne Brigade and a battalion detached from the 24th Mechanized Brigade. Both units were reportedly cought in the open by the Grad barrage, losing (in 3 minutes!) 35 dead, 93 wounded, 30 combat vehicles including tanks, ifv's and apc's.
Word of warning about question of units size during ukraninian conflict - official designations should be treated as rather misleading. Usually units operated not fully completed, understrenght both in terms of manpower and equipment.
Generally lessons from war in Ukraina can be boiled down to few things:
1 Artillery, augmented with uav's recon (Russians/separatists reportedly had used more than 10 types of uav's) IS THE KING of battlefield. Especially rocket artillery using thermobaric and cluster ammunition. Static defenses were useless against concentrated barrages, APC's and older IFV's (BMP1/2) were not protected enough against submunitions and even shrapnels, even tanks were vulnerable. Units cought under barrages were suffering loses causing the combat-incapable.
I can find some precise data, but reaction times of russian regular rocket artillery units were apparently shocking to american observers.
2 Tank are practically impervious to infantry light AT weaponry. Even DC warheads don't guarantee an effective attack. Top-attack is the way to go, but with proliferation of active defense systems, it will be rendered ineffective too. The best way to destroy a tank is to use an another tank. But when Russian used their T-72B3's and T-90's (the latter in a very limited way) they proved superior to ukrainian T-64/T-64BM Bulats. From reports it looks that russian passive defense systems on tanks rendered all ukrainian ATGM arsenal ineffective.
3 UAV's (especially smaller ones) are surprisingly resistant to the AA fire. Ukrainians usually were engaging russian uav's using 14,5mm, 23mm and 30mm autocannons with very little success. MANPADS and SAM's are also not very effective due to uav's low radar and ir signature. On the other side, Russians very effectively used electronic warfare (GPS spoofing or jamming and other means) against few ukrainian uav's being used (sometimes these were simple commercial uav's fitted with cameras).