The person posting this issue is running 2.0.0.

Are you running plugin version 2.0.0?

Have you wiped your config after you updated to plugin version 2.0? If not, please do, and get back to me. You can read the update notes for 2.0 here, which explains why you need a new config. 

Just repeating what i answered in another post,
Well guys it works for me with no problems, When the plugin updated and i saw that the main size config would be in the data file I just copy/pasted my original "config" into the data file, I changed the "new" config file to what i wanted , when i checked the data file i noticed that some items were stacked larger or smaller ( because what "group" they were in) than i wanted and changed them one by one to what i wanted,
This update is great as i can now stack electrical and diving as well as weapons and tools,
I have my resources stacking at 600000, medkits at 50, weapons at 5, I dont bother using chat or rcon to update the files it is much easier (because of the amount of items) to copy the data file into a new text document, take my time editing it , check it with json validator and then copy paste it back into the data folder,
I do this also because my Streamline dashboard will close down after about 5 minutes which is bad if you are editing a large file, :)

If its not working validate the file because if there is an error in your edit it will revert to default,

I forgot to mention that this error also comes from an error in your data file. Have you manually edited your data file recently, and maybe have forgotten a comma or something? 

Got it working

Thanks everyone I realized the dev put instructions to delete our configs after last update and had missed it. Sorry for spreading false information. Anyone else having the problem, just delete your config and reload! Thanks <3