Problem with iPhone 11 battery tag on flex

I’ve replaced the battery in an iPhone 11 using the battery tag on flex from JC. Once the phone drops to exactly 70% from a full charge it crashes, bootloops for a few second then restarts and will then run fine until the battery dies. I’ve ran this test several time with the same results. If I remove the tag on flex, the battery works perfectly, no crashing.

I’ve transferred the BMS onto the new battery and activated the tag on flex. I’ve tried restoring via DFU mode, and using a second tag on flex with no luck.

Was wondering if anyone had any ideas/suggestions?

Thanks in advance for any advice!