In my case this test may help you

16 19
1 2
2 3
3 4
4 5
5 1
1 6
6 7
7 8
8 9
9 10
10 6
5 11
11 12
12 13
13 4
3 14
14 15
15 16
16 2

The sequence of contraction affects the solution if you do not repeat the process after release the blossom.

if you contract (6,7,8,9,10), (4,5,11,12,13), (2,3,14,15,16) first
   you get maximum matching.
but if you contract (1,2,3,4,5) first and don't repeat the process after release it
   you don't get to the maximum.

Hope this helps.

Thank you for this case! I didn't realize that the blossoms should be reset in each iteration.