Downloaded latest trainer from here www.cheathappens.com/19517-PC-Witcher-3-The-Wild-Hunt-trainer and successfully ran it on Windows 10 64bit.
These trainers do not have any dependencies and they do run on 64bit without any issues. You havent said what your AV is but as of now my only guess is that it has something to do with it since these trainers aren't signed unlike our newest trainers.
Not sure what happened but now the trainer works fine... IDK. I did just recently remove some hidden bloatware AV software it took 3 reboots to get rid of. Maybe that was doing something? as for what AV I do normally use, Windows AV. I also have used Charter ISP AV software in the past on my old rig.