Will this issue ever be fixed?
This can’t be answered here, you would have to ask Sony because it’s their bug. Honestly, I doubt they will fix it, but there are chances that the bug isn’t present in newer (Sony-branded) Android versions anymore.
If not, the alternative address book to use ‘True Contacts’ has not been updated for more than a year and i am using android 6.0.1
Is it usable? Otherwise, there are plenty of address book apps in the stores, but I haven’t tried them personally. Of course, you can also use a custom ROM like CyanogenMod which will fix the problems caused by proprietary Sony code.
… please could you fix the bugs?
As said above, this is a Sony bug. Please ask them to fix the bugs.