I found this in the manual
Heating Tank - 65C, but above 55C only with a backup heater. Mine doesn’t even go to 50C without a lot of flickering.
I tried enabling the internal heater (I had it on for heating, not DHW), but it doesn’t look like it’s turning on at all, maybe because it’s not even reaching 55C.
I’m emailing panasonic at this point with what I have and see what they can offer.
I interpret the Table slightly differently. The left hand column is called Water Outlet Temperature (i.e. LWT), not DHW tank temperature. To me the bits that you’ve highlighted say that you can get your LWT up to 65degC (though only 55degC without an immersion heater), but nothing about the maximum DHW tank temperature that this would correspond to.
Good move to email Panasonic, though, and good luck 
!
I’d interpret it to mean 55C max LWT from the HP itself, with 65C possible using the in-HP backup heater, which is distinct from the in-tank immersion/booster heater. My system has both.
The hottest my DHW-related LWT has ever got is 58C, on a disinfection run, the immersion took over at that point.
