I managed to get the artifacts challenges 6.1, 6.2, 6.3 done the hard way by investing a lot of energy and time before the 1.8 patch. 

However after the 1.8 patch it seems there still is something very odd happening with the probabilities of 4* Life Set Gauntlets with HP (%) in artifact Challenge 7.3. 

7.4 (chest plate with hp%) and 7.5 (boots with hp%) were clearable in a reasonable amount of tries. 

However it seem the hp % gauntlets have an especially low drop rate compared to other stats.

I first tried in more than 100 runs on Kaerok Castle Hard. 

After that I got so frustrated that I played trough the whole Hard campaign just to reach Kaerok Castle Stage 4 on Brutal in the hope the higher chance of dropping 4* would help. 

The following Life set gauntlets dropped: 

5* Attack x1 

5* Attack % x2 

5* Defense  x1 

4* UC HP % 1x 

4* UC Attack 1x 

4* UC Defense  1x 

4* UC Defense % 1x 

4* UC Crit Rate % 1x 

4* HP 4x 

4* Attack  % 4x 

4* Defense 8x 

4* Crit Rate % 3x 

4* Crit Damage 2x 

From 29 4* items only 1 HP % item dropped. 

This selection ignores 3*, shards, champion drops. 

What seems oddly low is the probability to get a HP % drop in comparison to all other stats. 

... 

If you toss a coin you have a 50% chance to get head or tail. 

If you toss a dice you have a 1/6 chance to get a six. 

... 

Why is the probability of getting a HP % gauntlet significantly lower as getting any other stat on the gauntlet? 

Is this working as intended?