This time I watched very carefully. Stock A's dividend received. Instead of "DIV" and "BOUGHT" (for the new reinvested shares) transactions like all the times past for Stock A, now Vanguard is downloading "DIV" and "MISC EXP" (to get rid of the cash balance, albeit incorrectly now without the subsequent buy) transactions. Ergo, no purchase transaction to pick up the new shares.
Net effect is that the shares owned do not match between Q's portfolio and the Vanguard account website, and a Placeholder dialog screen is offered instead. Yech.
Time to call again and complain. Others seeing the same thing?