it might be switching between 2 towers for whatever reason..one drops a bit compared to the other tower so the phone jumps between the 2. might have asked this already but did you turn off/uncheck the connections optimizer/automatic connections? and what do you have the mobile connection set to? automatic? CDMA/LTE?
2 odd things. Connections optimizer has turned itself back on and I no longer have Autotamatic... Its set to Cmda/lte with only other option cmda
it doesnt give you the option for automatic anymore? thats weird. if you have insurance on the phone i would take it into one of the service and repair stores to have them give it a once over. my Flex2 isnt even charged anymore so i cant check against it..plus its not fully caught up update wise so i would have a ways to go before i could do any testing lol.