Thanks for the information, now it seems more clear what could happen.
The (re)routing requests contain also the location’s heading (coming from GPS).
Navigation gets the (re)routing response and auto-announces the 1st instruction.
Navigation continues. If user keeps being off route then more reroutings happen.
Automatic 1st voice instruction should probably be omitted
and only the programmed instructions must be announced.
(then such confusion can be avoided)