F5 DNS vs LDNS , client bounce from site to site

hi everybody , i have F5 DNS work as GSLB for 2 sites DC&DR ( active|active) with toplogy load balance mechanism and presistance profile enabled , some client accessing specific website through internet is geting fliped from dr node to dc node , i opened case with support ,they revise configuration succsuffly and conclude the below :

 

The issue is likely to be external.(For instance, the isp(DNS) maybe caches and providing round robin answer to client system or isp may have more than 1 dns server in different location). if the issue is intermitten, the best next action to take is to investigate between client to the isp(DNS).

 

if the issue is happening because the ISP is returning the different address to the client, the place to investigate is on with the ISP, there is nothing much we can do here but you will need to check with the ISP.

 

SO , does any one face this issue before ????if it's external issue it must been happen to anyone before any advice will be helpfull Thanks all text