Looks like this has to do with us resetting the Hydra stats in the last patch. Please try the following
1) Move unit to your homeland
2) Log out, log back in
3) Reset Hydra Unit stats completely - using Reset button
4) Log Out, log back in
5) Allocate Hydra skill-points how you see fit
6) Log Out, log back in
It should work fine now. We`ll have a fix for this in the next patch anywho - thanks for letting us know.