The following C++14 source code, which is also attached as `mwe.cpp',
shows the indentation problem:

--8<------------------------------
#include <vector>
#include <iostream>

static std::vector<std::vector<unsigned>>
fn(std::vector<std::vector<unsigned>> data) {
  return {
          {1, 2, 3},
          {4, 5, 6},
          {7, 8, 9},
  };
}

static std::vector<std::vector<unsigned>>
fn(unsigned n, std::vector<std::vector<unsigned>> data) {
  return {
          {n + 1, n + 2, n + 3},
          {n + 4, n + 5, n + 6},
          {n + 7, n + 8, n + 9},
  };
}

int main() {
  /* Expected indentation */
  fn({
      {1, 2, 3},
      {3, 4, 5},
      {6, 7, 8},
    });
  for (const auto &v : fn({
                           {3, 4, 5},
                           {6, 7, 8},
                           {9, 10, 11},
      })) {
    for (const auto &a : v) {
      std::cout << a << '\n';
    }
  }
  /* End: Expected indentation */

  /* Problem */
  fn(20, {
      {1, 2, 3},
        {3, 4, 5},
          {6, 7, 8},
            });
  for (const auto &v : fn(20, {
        {3, 4, 5},
          {6, 7, 8},
            {9, 10, 11},
              })) {
    for (const auto &a : v) {
      std::cout << a << '\n';
    }
  }
  /* End: Problem */
}
--8<------------------------------

To fix the problem, I make the following patch:
--8<------------------------------
diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index 05b391a..077e9c9 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -10387,6 +10387,7 @@ comment at the start of cc-engine.el for more info."
               (eq (char-after) ?\())
          (setq braceassignp 'c++-noassign))
         ((looking-at c-pre-id-bracelist-key))
+        ((looking-at ",\\s *"))
         ((looking-at c-return-key))
         ((and (looking-at c-symbol-start)
               (not (looking-at c-keywords-regexp)))
@@ -10398,6 +10399,7 @@ comment at the start of cc-engine.el for more info."
            (and (c-go-up-list-backward nil lim) ; FIXME!!! Check
`lim' 2016-07-12.
             (eq (char-after) ?\()))
           ((looking-at c-pre-id-bracelist-key))
+          ((looking-at ",\\s *"))
           ((looking-at c-return-key))
           (t (setq after-type-id-pos (point))
              nil))))
--8<------------------------------

Any better suggestion as to how to fix the problem?

Thanks.

In GNU Emacs 27.0.50 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
 of 2017-09-27 built on lgw01-amd64-052
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
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--
Best regards,
Tadeus