DCPROMO 2008 R2 OUT - SLOWNESS AFTER FUNCTIONAL LEVEL RAISED TO 2012 R2

hi,

Variety of performance problems after dcpromo out a 2008 r2 dc. General slownes of apps edms - some scripts run slower.
Very hard to pinpoint cause. ran dcdiag all clear - all DNS reference to old dc gone - no legacy mapped drives or any connection to old dc to be found'
raised functional level of domain to 2012 r2  - we have 2 dcs very simple single site domain. now just 2 2012 dcs

the fsmo roles all accross to 2012 r2 dc. - 1 thing that did happen is the fsmo holder server had many patches applied not the wannacry patch that causes slowness.
the point is is that the 2012 r2 dc is just that just a dc with dns - its not used for anything else. i dont see how it could cause slowness accross applications
I have read that SMB signing can cause slowness - when you run 2012 - thing is the 2012 dc/s have been in place for years no issue.

before we dcpromoed out the 2008 rs server we turned it off for 2 weeks - and had no issues. Its only post the dcpromo and 2012 functional level up and perhaps the patching of the dc that the weird sslowness in some apps has raised its head.

what can raising the functional level and dcpromo do to slow the network. ?? thanks