Auto Target Experience Uplift Dropped After 50:50 Split from 90:10 Split

Hi,

Here is the scenario,

Activity Type : Auto Target
Business Questions:
We are running an auto target campaign with 90:10 ratio to split the traffic, which means 90% traffic to control experience and remaining 10% traffic to Exp B, C, D, and E, the campaign ran for 3 weeks and we identified the clear winner is Experience C with 21% uplift with confidence level 99.9%

then business split the traffic to 50:50 ratio which means 50% to control and remaining 50% traffic to Exp B, C, D and E within the existing campaign activity. Uplift got dropped and the result was 3% 0.5% 2% and 2% respectively (Exp B,C,D, and E)

What could be the reason for uplift drop after the 50:50 split?

Your thoughts appreciated.

Thanks