Hmm so three commissioned DDGs are back at the shipyard presumably for some degree of work. Impossible to rule out the possibility of issues that have come up during trials and operation, but then again I'd hazard against jumping to conclusions about how serious the work is and whether it is symptomatic of any serious issues.
A good gauge would be if we knew how long each ship was back at the shipyard for, but we don't have anything like constant monitoring of the shipyard to make that call.
I wasn't around here when the first 052Bs and 052Cs were commissioned back in the 2000s, does anyone remember if they came back to their shipyards occasionally to have work done in the year or so after their commissioning?