i don't think you understand how drop rate works in this game.
First of RNG IS RNG get over it. No bug you are just complaining over nothing; over something that has happened to everyone over the course of 3 year since RoS launched with the perma 100% drop buff (go look this fact up. On launch the drop rate of legendaries were much lower).
each of their own drop rate. from base they have a 10% chance to be ancient and approx 1% to be primal (if you solo GR70).
Helm, shoulders, chest, gloves, pants, boots, weapons, off hands, rings, and amulets all have separate drop rates.
with in each sub group you have specific rarities per item. Example for rarest items in the game: Star metal Kukari, Furnace, Star of azkarath, Kridershot, Istvan's paired blades, etc (having 1.64%-3.28%).
How do you mitigate this? The answer is simple play the game more often. Gain more shards to spam Kadala. Do more rifts to gain more mats to use at the cube. Each time an item drops, it's like playing bingo. 1/100 chance means within your pool of drops, you have 100% chance to get all 1's in the binary code. But you also have a chance to get all 0's in the binary code. The fact you are complaining about this now means you have never gotten 5 straight fails on a 90% chance of upgrade on a GR clear. This is what 90% looks like 1 1 1 1 1 0 1 1 1 1. That means every time you spun for bingo you magically hit that 0 five times.