Bluetooth connection with S24 keeps dropping

I was on FR935 with excellent connection to my S24 phone.

Just got the FR965 and experience the common bluetooth connection problem.

After 3 hours of fiddling, I managed to pair the FR965 and S24 when I kept them at around 40-50cm apart.

Even after pairing, the sync is a pain as it keeps getting disconnected no matter what distance apart. I can't even customise the watchface without it disconnecting every 2-5secs.

Here is the question: What is causing FR965 BT to not work well when less than 50cm apart and what is causing it to disconnect every 2-5secs?