apple watche keep losing bluetooth connection

Dear all

I purchased an Apple watch series8 several months ago and found out that sometimes bluetooth connections will be lost frequently. i called apple support and asked for help and they told me upgrade software of both devices and reset the network and delete all the vpns but it didn't help. 

i bought series ultra2 yesterday and found out this happens again. i called apple support and they told me do reset factory by computer and it didn't hep either.

i asked some of my friends to check their phones and we found out when you turn off wireless of your iPhone the bluetooth connection connect and disconnect frequently.

i have checked below test and had same results.

iPhone 12 pro max with apple watch series 8.

iPhone 12 pro max with apple watch series ultra 2

iPhone 13 with apple watch series 8.

iPhone 12 pro max ( different from above iphone ) with apple watch series 2.

i can also send you my screen recordes