Minecraft v1.15.2
End Reborn v0.5.8

The log is printing out quite a few tag errors related to Endorium and Ogana Fruit, provided in the link below.
Log

Seems forge:mod_loaded condition does not work with tags. Okay, in the next update will be fixed

If you add an optional category and leave the values category blank, that should fix it. The optional value will only load if the item exists, so it won't print any errors if Mekanism isn't installed.

Such as

{
  "replace": false,
  "values": [ ],
  "optional": [
    "endreborn:endorium_dust"
  ]
}

Thanks, I'll try to use this format