all is possible.
with 19 speed secondary 5* mod you should get a +20 speed after slicing.
if you still have 19, contact ea/cg.
i had another case last year, when i got a full gear 12 piece as a sith-raid reward. but: it wasn‘t the piece, that was shown in the reward-box. i only knew it could help my pilot biggs. later it was gone.
with the help of cg-carrie we found out, that the reward changed.
so i believe 100% what you wrote, but please contact support, because tomorrow another player can have this problem. i hope, the technic-profis can find the problem.
would be nice if you can report in this threat, how the story ends. normally they are interested to solve such problems fast.
and
since my experience last year i make screenshots of all hsr-rewards and also before your post of every slicing to 6*