After loading into the instance, then choosing my role (I always choose Scout) before the start of the match, then once the match starts, my role is automatically changed to either Support or DPS.
This occurs whether I choose my role from the #9 skill slot or by talking to the Snowman NPC.
Out of the 30 or so matches, its happened about 6 times now, seems to be more frequent within the last hour.
It only happens at the start. Once I’ve choosen the Scout role again its fine for the rest of the match. Its like the game forgets I made a selection and choose one for me.