False positives are a common occurrence with trainers, no matter where on the internet you get them from. Even if the trainer was okay before, the antivirus can randomly decide another day that it doesn’t like it.
It is purely because of the way trainers work, which is by injecting values into your PC’s RAM. In WeMod’s case, it is also sometimes flagging the security encryption that WeMod uses to protect the trainers from being ripped and re-uploaded to shady websites, because it cannot identify the security encryption (which is a good thing). Add WeMod as an exception in your antivirus and the problem should be resolved.
Further reading: Windows Defender marked WeMod as a Trojan.