The bug report is it not getting the composite armor, as far as my source tells me ( Modern Russian Tanks & AFVs: 1990-Present (Technical Guides) ) this little bugger should get composite armor over the pre existing RHA. To reaffirm my thought that this is a bug, lets look at the in game stats; the BTR-82AT is 16 tons (without slat armor) while the BTR-80a is 14.6 tons. Where did it acquire 1.4 tons you might be asking yourself, *Composite armor*.
Now I don't really have more sources, but if the composite armor does not get added some of that extra weight should get removed and the speed should get put up to like 85ish KPH. (the BRT-80a can go 87)
Side note:
I have a genuine question, why does the BTR-82AT not get moved up in BR and get the APDS-FS? I would recommend putting it at 9.7 if this were to happen. Just curious what’s stopping it from getting the Dart round it should get?