I can say it will be around 90 run before effect worn out.
I broke about 60 gems for testing it during that time.
Well I broke those gems to answer my curious, not recommend to do the same LOL.
From the FKG Support Team:
So, just a bug then; I'll try to reproduce it this weekend.Hey Taon,
There is no secondary limit on the number of runs. As mentioned in our previous reply, if it happens again, try to send us a screenshot and we'll investigate further as for now we are unable to reproduce the issue.
Regards,
Flower Knight Girl Team
Good to know it's bug.
Hope they already fix it, if not it's mean this bug stay for very long f*cking time.