Cannot seem to use more than 10 grass types

Using the material editor , when i add the 11th grass type it wont place the grass no matter what i do. There a similar question for which i tried the fix but nothing happened.

Any suggestions ?

Yes, there is a limit to the grass tool.

The patch from your link does still work but i had to manually copy the changes from the last patched version of LandscapeGrassWeight.usf into the current UE4 4.20 LandscapeGrassWeight.usf.
The important part starts right after

#endif // NUM_MATERIAL_OUTPUTS_GETGRASSWEIGHT > 6

Here is the whole 4.20 file patched: // Copyright 1998-2018 Epic Games, Inc. All Rights Reserved./*============== - Pastebin.com