This game has a lot of issues if you have OneDrive enabled. I always turn off OneDrive and remove its folders, which can need some registry editing. (Registry editing is
not something I recommend to anyone not familar with it.)
Anyway, your addons should have a folder hierarchy similar to this:
C:\Users\{Your Username Here}\Documents\Elder Scrolls Online\live\AddOns
Make sure the addons are installing in the correct location.
For HarvestMap, you also need
HarvestMap-Data. You have to go into its folder and run the DownloadNewData.bat file. Otherwise HarvestMap won't automatically supply you with harvesting node locations. If you don't run the "bat" file, the addon will only show icons for things
you have actually harvested since running the addon.