Well, while the latest 8.10 SDBG64 is way better then previous ones it is still not fully fixed.
It works when all large problems are cleaned preliminary with 32 bit SDBG but often fails without preliminary cleaning. Such cleaning is not always possible when you substantially depart from older 32bits.
It may display the lines you step incorrectly, may jump crazily up or down into wrong place, and with unknown problem all variables inside the subroutine could be displayed as -2.3212313d-308 (something UNDEFINED may be causing that) , offending lines still may not be shown correctly, parameters are not shown (with or without /full_debug)
I hope company did not stop working to further improvement of SDBG64.