[Gameplay] Mordekaiser's Q not dealing physical damage component of each strike consistently

I went into a custom game to test out if I can get Mordekaiser's 3rd Mace of Spades strike to work simultaneously triggering the tri force sheen effect on that third strike.

I found that not only was the third strike not triggering any physical damage component sometimes, but all of his other strikes seemed random in whether or not the physical damage component was occuring with each strike. Every Q strike was showing the magic damage component as expected but sometimes there was no physical damage component.

My steps taken were, after restarting my client due to buttons not working, I went into a custom game, added 5 beginner bots to the enemy team: Garen, Xin, Fizz, Shyvana, Master Yi. and proceeded to champ select where I chose mordekaiser with flash/teleport, 30 armour, 12 magic resist as my runes, my APC mastery page and when I got into game I rushed for a tri force using saphire crystal component first into sheen then longsword and went straight into tri force from there and then went into steraks gage.

In terms of attempting to accurately reproduce the bug, it seems to occur when the strike will easily kill the minion/monster or champion.