You're probably having issues with updating your mods. Otherwise, why would you be reading this? I had issues too and spent quite a while fiddling with .mod files until I decided to go to the dev diary on the topic[forum.paradoxplaza.com].

The second post is titled Instructions for Modders with an "Updating mods" section. That contains all the info you'll need. I've pasted the contents here:

Originally posted by BjornB:

Currently most mods have one mod descriptor, usually ModName.mod. This is now split in two: ModName.mod which needs to have the name entry and a path or archive entry and descriptor.mod inside the mod folder, which also needs the name and has everything else. Updating them means creating this descriptor.mod and copying most things from ModName.mod into that. So essentially: Keep name and path or archive in your current .mod and move everything else into descriptor.mod inside the mod folder.

• If you have an issue with creating the descriptor file you should note that you can simply copy the content of the .mod file into the descriptor - this should not cause an issue.
  
• Remember that the descriptor.mod file should be inside the mod folder.
  
• If you get a credential error when attempting to upload a mod make sure you have something in the description section - you can simply put your current description from the workshop here. If your workshop description is to long for this then update the mod with anything in the description box and then add your full description later.

And here's a step-by-step walkthrough if you need more guidance:

1. Go into your Documents\Paradox Interactive\Hearts of Iron IV\mod folder.
   
2. Copy and paste the .mod file of the mod you want to update into that mod's individual folder.
   
3. Rename the new .mod file "descriptor.mod".
   
4. Open the HOI4 launcher, go into the Mods section, and click on the Mod Tools button.
   
5. Go to Upload a mod, select the mod, and enter the mod's description (since you're updating it, paste the workshop description and make any needed changed).
   
6. Wait for it to upload, and you're done.

You can also change the version to "1.8.*" to avoid having to update it again for every hotfix. When you're updating a mod, it won't show anything under Version. This is fine, it'll still upload. Once you've finished, you can repeat the process with any other mods you want to update, and they'll show as compatible on the launcher.

Note: The .mod file inside the Hearts of Iron IV\mod folder MUST NOT be saved with a byte order mark (BOM) if it is saved in UTF-8 format. Either save it as UTF-8 without a BOM, or save it with ANSI or ASCII text encoding if the file does not include any non-English characters. (Thank you Mr Tsubodai for pointing this out in the comments.)