Tenacity not preventing debuffs

Product: Star Wars: Galaxy of Heroes
Platform:Apple iPhone
What type of device are you experiencing the issue with? iPhone 6s
OS Version 13.5.1
Ally Code: (Find it here: http://bit.ly/AllyCode ) 856563735
What type of issue do you have? Gameplay
How often does the bug occur? Rarely (0% - 9%)
Summarize your bug This round of GAC (oct 9) my relic 3 Malak with 163% tenacity received the tenacity down debuff from my opponent‘s (ally code 96311181) Night Sister Zombie that had 17% potency Ultimately this allowed his Nightsister team to stun lock my Malak cost me the battle and the GAC round (which as is I have lost by four banners)
Steps: How can we find the bug ourselves? Test high tenacity Malak solo’s against low potency Night sisters and see if eventually a debuff lands when it should not
Connection Type Wifi
Please select your region North America
Country United States

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This round of GAC (oct 9) my relic 3 Malak with 163% tenacity received the tenacity down debuff from my opponent‘s (ally code 96311181) Night Sister Zombie that had 17% potency

Ultimately this allowed his Nightsister team to stun lock my Malak cost me the battle and the GAC round (which as is I have lost by four banners)

my understanding is the chance to resist a debuff is Max (15%, your Tenacity -opposing potency) which should have made it impossible for tenacity down to land